Titanylphthalocyanine crystal and method of producing the titanylphthalocyanine crystal, and electrophotographic photoreceptor, method, apparatus and process cartridge using the titanylphthalocyanine crystal

ABSTRACT

A titanylphthalocyanine crystal having an X-ray diffraction spectrum having plural diffraction peaks and a primary particle diameter not greater than 0.2 μm, wherein a maximum diffraction peak is observed at a Bragg (2 θ) angle of 27.2±0.2°; main peaks are observed at 9.4°, 9.6° and 24.0°; and a minimum diffraction peak is observed at 7.3°; and preferably no diffraction peak is observed at an angle greater than 7.3° and less than 9.4° when a specific X-ray of CuKα having a wavelength of 1.542 Å irradiates the titanylphthalocyanine crystal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a titanylphthalocyanine crystal and amethod of producing the titanylphthalocyanine crystal, and to anelectrophotographic photoreceptor, method, apparatus and processcartridge using the titanylphthalocyanine crystal.

2. Discussion of the Background

An organic pigment has been used as a filler for a coating materialsince comparatively a long ago. In particular, the organic pigment hasthe advantage over an inorganic pigment in its abundance of colorvariation. Further, recently as an application of the organic pigment, avariety of materials have been produced because it was spotlighted as amaterial for an organic photoelectric transfer device.

Almost all methods of forming a film including the organic pigment arewet coating methods. It is not exaggerated to say quality of a filmcoated by the wet coating methods depends on quality of a dispersionliquid including the pigment. Dispersibility of the pigment in thedispersion liquid is one of essentials for the quality of the dispersionliquid. Therefore, a good dispersion liquid includes the pigmentsufficiently dispersed in a vehicle and continues the dispersed statusfor a long term.

Recently, digital electrophotographic methods prevail, and particularlya negative and positive development (reverse development) is mostlyused. In a case of the negative and positive development, a part of aphotoreceptor used in the electrophotographic method is irradiated byimagewise light and a potential of the part decreases to form a tonerimage thereon. This is performed in consideration of a longevity of alight source and fatigue of the photoreceptor because writing ratio ofan original copy is more or less 10% at most. However, background of aproduced copy corresponds to a non-irradiated part (high potential part)of the photoreceptor, and when a photosensitive layer (particularly acharge generation layer) has a coating defect, a background portion(white background portion) of the photoreceptor which should havemaintained potential decreases potential, resulting in occasionaloccurrence of point defects such as background fouling and black spots.These defects are occasionally mistaken for points in drawings andperiods and commas in English drafts, and it can be said that thedefects are fatal defects as images. Such point defects

are often caused by a layer constituted of dispersed film includingpigments, etc. Therefore, in order to decrease the point defects, adispersion liquid having good dispersibility of pigments, etc. has to beproduced. A particle size of the pigment in the dispersion liquid ispreferably as small as possible, and a pigment having a primary particlesize not greater than about 0.2 μm considerably decrease the pointdefects as mentioned above.

In order to produce such dispersion liquids, a variety of dispersers anddispersion systems and methods of increasing dispersibility have beensuggested. For example, any of Japanese Laid-Open Patent PublicationsNos. 4-373362, 5-188614, 7-289870, 8-44086, 8-123945, 8-272111,9-211873, 11-30871, 11-258827, 2000-126638, 2000-181104, 2000-281931,2001-265027 and 2001-290292 discloses a technology to miniaturize(reduce a particle size of) synthesized large average-size pigmentparticles in a dispersion liquid as small as possible using a variety ofdispersers, dispersing conditions or improving the dispersers andconditions. It can be said that these dispersion methods are goodtechnologies in terms of efficiently dispersing the pigment until thepigment has the primary particle size. However, it is quite difficult toreduce the particle size more than the primary particle size, and alimit of the particle size in the dispersion liquid basically depends onthe primary particle size of the pigment. Methods of pulverizing theprimary particle with an enormous energy are included in the methods,but these break the crystal and have problems such as deterioration ofdispersion efficiency and transform of the crystal form as mentionedlater.

On the other hand, as a useful charge generation material,titanylphthalocyanine is known. The titanylphthalocyanine is a polytypiccrystal pigment including many crystal forms as an aggregate even whenhaving the same formula. Particularly, a titanylphthalocyanine crystalhaving at least a maximum diffraction peak at of a Bragg (2 θ) angle of27.2±0.2° when irradiated with a specific X-ray of CuKα having awavelength 1.542 Å has significantly a high photo carrier generationefficiency as a charge generation material for an electrophotographicphotoreceptor among polytypic crystal pigments. However, thetitanylphthalocyanine has a quasi-crystallinity and easily transforms toother crystal forms. When an excessive energy is applied to the crystal,the crystal easily transforms to a titanylphthalocyanine crystal havinga maximum diffraction peak at Bragg (2 θ) angle of 26.3°. Because thiscrystal has considerably a lower photo carrier generation efficiencythan the above-mentioned crystal, when even a partly transformed crystalis used for a charge generation material for a photoreceptor, problemssuch as deterioration of photosensitivity and increase of residualpotential in repeated use occur.

When the dispersion condition is tempered to prevent this crystaltransform, the resultant dispersion liquid includes a pigment having alarge particle diameter or remaining coarse pigment particles. When sucha dispersion liquid including a pigment having a large average particlediameter is used, surface area of the total charge generation materialsbecomes small, and it becomes difficult for the material to give andreceive a charge to and from charge transport material, resulting inproblems such as deterioration of photosensitivity and increase ofresidual potential in repeated use of the resultant photoreceptor occur.When the coarse particles remain, the resultant image has problems suchas background fouling and black spots occur in the negative and positivedevelopment.

As just described, in the dispersion of the titanylphthalocyaninepigment particles, stability of the crystal form and miniatulization ofthe particles have a trade-off relation and means to easily solve thisproblem have not been available.

As another method of reducing the particle size of the pigment in thedispersion liquid, a method of using a pigment which can easily bedispersed, i.e., which has significantly a small primary particlediameter can be considered. In this method, a pigment previously havinga small primary particle diameter is synthesized to obtain a dispersionliquid including a pigment having a small particle diameter withoutapplying an excessive energy to the pigment. This method not onlyimproves dispersion efficiency but also can be considered assignificantly an effective method when using a pigment in which acrystal easily transforms such as the above-mentionedtitanylphthalocyanine.

However, approaches in terms of pigment synthesis have hardly been seenso far. Only Japanese Laid-Open Patent Publication No. 2000-239556discloses a method of producing a dispersion liquid using means ofcombining a crystal conversion and dispersion means. This method canform a dispersion liquid including a pigment having a primary particlediameter, which is formed by the crystal conversion. However,considering the dispersion liquid is used for a coating liquid, acrystal conversion solvent is not limited to a suitable coating solventand the method has a drawback of having a restriction in coating. Inaddition, because the dispersion liquid cannot be stored as a pigmentpowder, the method also has a drawback of having a restriction instorage.

Because of these reasons, a need exists for a titanylphthalocyaninecrystal having a small primary particle size and a method of producingthe titanylphthalocyanine crystal to prepare a dispersion liquidincluding a pigment having a small average particle size without acrystal transform of the titanylphthalocyanine crystal which is quiteuseful as a charge generation material for an electrophotographicphotoreceptor.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide atitanylphthalocyanine crystal having quite a small primary particlediameter and is capable of preparing a dispersion liquid including thetitanylphthalocyanine crystal, in which the crystal stability is highand the particle size is small.

An other object of the present invention is to provide a method ofproducing the titanylphthalocyanine crystal.

Yet another object of the present invention is to provide a stableelectrophotographic photoreceptor using the titanylphthalocyaninecrystal and producing less abnormal images without loss of highsensitivity, deterioration of chargeability and increase of residualpotential in repeated use.

Further, another object of the present invention is to provide a stableelectrophotographic method, an electrophotographic apparatus and aprocess cartridge therefor using the electrophotographic photoreceptor,which are capable of printing at a high-speed and producing lessabnormal images.

Briefly these objects and other objects of the present invention asherein after will become more readily apparent can be attained by atitanylphthalocyanine crystal having an X-ray diffraction spectrumhaving plural diffraction peaks and a primary particle diameter notgreater than 0.2 μm, wherein a maximum diffraction peak is observed at aBragg (2 θ) angle of 27.2±0.2°; main peaks are observed at 9.4°, 9.6°and 24.0°; and a minimum diffraction peak is observed at 7.3°; andpreferably no diffraction peak is observed at an angle greater than 7.3°and less than 9.4° when a specific X-ray of CuKα having a wavelength of1.542 Å irradiates the titanylphthalocyanine crystal.

In addition, titanylphthalocyanine crystal preferably has no diffractionpeak at 26.3° when irradiated with the specific X-ray of CuKα having awavelength of 1.542 Å.

These and other objects, features and advantages of the presentinvention will become apparent upon consideration of the followingdescription of the preferred embodiments of the present invention takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the detailed description when considered in connectionwith the accompanying drawings in which like reference charactersdesignate like corresponding parts throughout and wherein:

FIG. 1 is a schematic view illustrating a cross section of an embodimentof the photosensitive layer of the electrophotographic photoreceptor foruse in the present invention;

FIG. 2 is a schematic view illustrating a cross section of anotherembodiment of the photosensitive layer of the electrophotographicphotoreceptor for use in the present invention;

FIG. 3 is a schematic view illustrating a cross section of an embodimentof the electrophotographic apparatus for explaining theelectrophotographic process of the present invention;

FIG. 4 is a schematic view illustrating an embodiment of the chargerlocated closely to the photoreceptor, which has gap forming members foruse in the present invention;

FIG. 5 is a schematic view illustrating another embodiment of theelectrophotographic process of the present invention;

FIG. 6 is a schematic view illustrating an embodiment of the processcartridge of the present invention;

FIG. 7 is a schematic view illustrating an embodiment of the tandem-typefull-color image forming apparatus of the present invention;

FIG. 8 is a diagram showing an X-ray spectrum of the dry powder of waterpaste of the titanylphthalocyanine pigment;

FIG. 9 is a diagram showing an X-ray spectrum of thetitanylphthalocyanine crystal prepared in Example 1;

FIG. 10 is a diagram showing an X-ray spectrum of thetitanylphthalocyanine crystal prepared in Comparative Example 1;

FIG. 11 is a diagram showing an X-ray spectrum of thetitanylphthalocyanine crystal prepared in Comparative Example 9;

FIG. 12 is a diagram showing an X-ray spectrum of thetitanylphthalocyanine crystal prepared in Measurement Example 1; and

FIG. 13 is a diagram showing an X-ray spectrum of thetitanylphthalocyanine crystal prepared in Measurement Example 2.

DETAILED DESCRIPTION OF THE INVENTION

Generally, the present invention provides a titanylphthalocyaninecrystal having quite a small primary particle diameter and a method ofproducing the titanylphthalocyanine crystal.

Various properties of an electrophotographic photoreceptor using anorganic pigment as a charge generation material (herein after referredto as a CGM) depend on a particle size of the CGM in a photosensitivelayer of the photoreceptor. For example, when a particle size of a CGMis large, deactivation probability of a photo carrier generated by theCGM becomes high inside the particle before transferred to a chargetransport material. In addition, when a particle size of a CGM is large,surface area of the total CGMs inevitably becomes small. Therefore, acontact amount of the CGM and a charge transport material becomes smalland a photo carrier injection efficiency to the charge transportmaterial lowers. Further, when a particle size of a CGM is large,probability of coating defect of a photosensitive layer (chargegeneration layer) becomes high and the resultant images tend to bedefective.

Because of these reasons, it is desired that a particle size of a CGM ina photosensitive layer (charge generation layer) becomes as small aspossible. Because a photosensitive layer (charge generation layer) isusually formed by a wet coating method, a CGM particle size in a coatingdispersion liquid forming the layer has to be small so as to reduce theparticle size of the CGM in the photosensitive layer.

A variety of dispersion methods are suggested to reduce the particlesize of the CGM in the dispersion liquid for coating the photosensitivelayer. However, a serious problem of any of the methods is how secondaryparticles which are agglomeration of the CGM are pulverized anddispersed to primary particles. These methods are designed to make theparticles close to the primary particles as much as possible with an

enormous dispersion energy or an extension of dispersion time, etc.However, the primary particle size is determined in synthesizing the CGMand it is difficult to make the particle size smaller than the primaryparticle size by an ordinary method.

On the other hand, a dispersion method capable of applying much largerdispersion energy to the particles than a ball mill method having beenused from a long time ago, is suggested. In addition, a method offurther pulverizing the primary particles is also developed recently.These methods pulverize a crystal itself to reduce the particle size ofthe CGM. This method can be said to be suitable for a CGM having ahighly stable crystal stability.

However, when organic CGMs are used, only specific crystal forms oftenmake specific performance even if they have the same formula. Such aspecific crystal form occasionally changes with ease due to a simplephysical or mechanical stress as well other than a chemical stress. Whensuch an excessive dispersion energy as pulverizes the primary particlesas mentioned above is applied to such a material, the crystal formchanges before the particles are pulverized. Consequently, it frequentlyhappens that a material which exerts a specific performance changes intoa material which does not sufficiently exert the specific performance.

A phthalocyanine crystal for use in the present invention, particularlya titanylphthalocyanine pigment crystal is a crystal polytypic material.Only a crystal having at least a maximum diffraction peak at a Bragg (2θ) angle of 27.2±0.2° when irradiated with a specific X-ray of CuKαhaving a wavelength of 1.542 Å especially has a photo carrier generationefficiency. Other crystal materials perform as CGMs, but do not haveproperties which are satisfactory to high-speed printing, smallerdiameters of photoreceptors and high stability in repeated use requiredby the present electrophotographic process. Therefore, theabove-mentioned crystal form can be said to be a specific crystal form.

However, the titanylphthalocyanine crystal having a maximum diffractionpeak at 27.20 has a quasi-crystallinity and is a material having a lowcrystal stability. Therefore, when a mechanical or physical stress asmentioned above is applied to the crystal, the crystal transforms toanother crystal form having a stable crystal form.

Although the titanylphthalocyanine crystal has such a high performanceas a CGM, miniatulization of the particles and stability of the crystalform have a trade-off relation and means to easily solve this problemhave not been available.

The present inventors analyzed a process of pulverizing and dispersingthe titanylphthalocyanine crystal in order to solve the above problem toobtain the following findings.

Namely, in the process of dispersing the titanylphthalocyanine crystal,when the crystal is dispersed so as to have a desired particle size, anexcessive dispersion energy has to be applied to the crystal because theprimary particles having a particle size larger than the desired sizeare present. In addition, there is a remarkable difference between anenergy required to disperse the secondary particles which areagglomeration of the primary particles and an energy to furtherpulverize an enormous primary particles. The former energy is notapplied to the crystal but to the dispersion until the crystaltransforms. The latter energy is applied to both the pulverization andcrystal until the crystal transforms.

The present inventors found that a dispersion liquid including atitanylphthalocyanine crystal having a small particle size and a highcrystal stability can be prepared without giving an excessive dispersionenergy to the liquid by miniaturizing primary particles of thetitanylphthalocyanine crystal as much as possible.

An average particle size of the primary particles of thetitanylphthalocyanine crystal in the present invention is determined bythe following method.

A liquid including a titanylphthalocyanine crystal subjected to acrystal conversion is observed by a transmission electron microscope(TEM); the TEM image is photographed as a TEM photograph; and 30titanylphthalocyanine crystals are selected at random to measure alonger diameter of each crystal. An arithmetic average of the longerdiameters of the 30 titanylphthalocyanine crystals is determined as theaverage particle size.

Next, the present inventors tried to synthesize thetitanylphthalocyanine crystal to obtain the following findings.

Namely, the titanylphthalocyanine crystal having at least a maximumdiffraction peak at 27.2° is typically synthesized withtitanylphthalocyanine having a lower crystal stability than thetitanylphthalocyanine crystal having at least a maximum diffraction peakat 27.2°. A method often used is to convert crude titanylphthalocyaninesynthesized in accordance with the law into amorphous or lowcrystallinity titanylphthalocyanine considered to have lowest crystalstability by a method called an acid paste treatment using a sulfuricacid, etc. A crystal conversion is performed on the amorphous or lowcrystallinity titanylphthalocyanine by various methods to obtain atitanylphthalocyanine crystal having a desired crystal form. A methodmost often used for the crystal conversion is a method of transforming acrystal with a proper organic solvent in the presence of water.

The present inventors paid attention to morphology of thetitanylphthalocyanine crystal particles before and after the crystalconversion. The above-mentioned amorphous or low crystallinitytitanylphthalocyanine subjected to the acid paste treatment isprecipitated in water having a low solubility from atitanylphthalocyanine acid liquid solution and has a small primaryparticle size. The amorphous or low crystallinity titanylphthalocyanineis usually formed of microscopic particles having a diameter about 0.1μm or less and a shape which is close to a needle although depending onthe conditions of the acid paste treatment. The titanylphthalocyaninecrystal subjected to the crystal conversion has a crystal transform anda crystal growth at the same time, and usually the crystal is separatedand filtered after the crystal conversion is surely performed.Therefore, the

titanylphthalocyanine crystal subjected to the crystal conversion hasconsiderably a large primary particles having a particle diameter offrom about 0.3 to 0.4 μm, and even about 1 μm. As mentioned above, it isfound that the primary particle size of the titanylphthalocyaninecrystal for use in the present invention is determined by the crystalconversion process.

A specific titanylphthalocyanine crystal preferably used in the presentinvention having at least a maximum diffraction peak at a Bragg (2 θ)angle of 27.2±0.2°; main peaks at 9.4, 9.6 and 24.0±0.2°; a minimumdiffraction peak at 7.3±0.20; and preferably not having peaks greaterthan 7.3° and less than 9.4°, and at 26.3° when irradiated with aspecific X-ray CuKα having a wavelength of 1.542 Å is disclosed inJapanese Laid-Open Patent Publication No. 2001-19871. However, when atitanylphthalocyanine crystal is produced in the condition disclosedtherein, the resultant titanylphthalocyanine crystal has a large primaryparticles and problems as mentioned above.

A method of dissolving a trade-off relationship between miniatulizationof particles and crystal stability in dispersing thetitanylphthalocyanine crystal is how small the primary particles thereofis synthesized.

As a result of a study in consideration of the above, it is found that atime of crystal conversion is set as short as possible, i.e., about lessthan 1 hour, and preferably less than 30 min although depending on thecrystal conversion conditions when a crystal conversion is performedusing the above-mentioned microscopic amorphous titanylphthalocyanine orlow crystallinity titanylphthalocyanine particles as a material with anorganic solvent in the presence of water, and that a desired crystalhaving microscopic primary particles can be separated and filtered fromthe organic solvent before the crystal grows, i.e., before the primaryparticle size grows to be not less than 0.2 μm.

Hereinafter, specific methods will be explained.

First, a method of synthesizing a crude titanylphthalocyanine crystalwill be explained.

Methods of synthesizing phthalocyanines have been known for a long time,and are disclosed in “Phthalocyanine compounds” published in 1963 and“The Phthalocyanines” published in 1983, which are written by Moser andother authors, and in Japanese Laid-Open Patent Publication No.6-293769.

For example, A first method is to heat a mixture of phthalic anhydrides,metals or halogenated metals and urea in the presence or no presence ofa solvent having a high boiling point. In this method, catalysts such asammonium molybdate are optionally used together. A second method is toheat phthalonitriles and halogenated metals in the presence or nopresence of a solvent having a high boiling point. This method is usedto produce phthalocyanine which cannot be produced by the first method,such as aluminium phthalocyanine, indium phthalocyanine, oxovanadiumphthalocyanine, oxotitanium phthalocyanine and zirconium phthalocyanine.A third method is to react phthalic anhydrides or phthalonitrile withammonia first to prepare an intermediate such as 1,3-diiminoisoindolineand to react the intermediate with halogenated metals in a solventhaving a high boiling point. A fourth method is to react phthalonitrilewith metalalkoxide in the presence of urea, etc. Particularly, thefourth method is significantly an effective method to synthesize amaterial for electrophotographies because chlorination (halogenation) ofa benzene ring does not occur.

Next, a method of synthesizing an amorphous titanylphthalocyanine (lowcrystallinity titanylphthalocyanine) will be explained. This is a methodof dissolving phthalocyanine in a sulfuric acid, diluting the mixturewith water and re-precipitating. An acid paste method or an acid slurrymethod can be used.

A specific method is to dissolve the above-mentioned synthesized crudetitanylphthalocyanine crystal in a concentrated sulfuric acid 10 to 50times as much as the crude titanylphthalocyanine crystal, optionallyremove insolubles with a filer, etc. and slowly put the mixture intosufficiently cooled or iced water 10 to 50 time as much as theconcentrated sulfuric acid to re-precipitate the titanylphthalocyanine.After the precipitated titanylphthalocyanine is filtered, thetitanylphthalocyanine is washed with ion exchange water and filtered.This operation is sufficiently repeated until the filtrate becomesneutral. Finally, after the titanylphthalocyanine is washed with clearion exchange water and is filtered to prepare a water paste having asolid concentration of from 5 to 15 by weight. Thus, the amorphoustitanylphthalocyanine (low crystallinity titanylphthalocyanine) for usein the present invention is prepared. The amorphoustitanylphthalocyanine (low crystallinity titanylphthalocyanine)preferably has at least a maximum diffraction peak at a Bragg (2 θ) offrom 7.0 to 7.5±0.2° when irradiated with a specific X-ray of CuKαhaving a wavelength of 1.542 Å. Particularly, half width of thediffraction peak is preferably not less than 10. Further, it isessential for the following crystal conversion that the primaryparticles have an average particle size not greater than 0.1 μm.

Next, the crystal conversion method will be explained.

The crystal conversion is a process of converting the above-mentionedamorphous titanylphthalocyanine (low crystallinitytitanylphthalocyanine) to a desired crystal form, i.e., a crystal formhaving at least a maximum diffraction peak at a Bragg (2 θ) angle of27.2±0.2° of when irradiated with a specific X-ray of CuKα having awavelength of 1.542 Å. Particularly, the titanylphthalocyanine crystalhaving main peaks at 9.4°, 9.6° and 24.0°, a minimum diffraction peak at7.3° and preferably not having peaks at greater than 7.3° and less than9.4° is preferably used. Further, the titanylphthalocyanine crystal nothaving a peak at 26.3° is more preferably used.

A specific method of obtaining such titanylphthalocyanine crystal is tomix and stir the amorphous titanylphthalocyanine (low crystallinitytitanylphthalocyanine) with an organic solvent in the presence of waterwithout drying the amorphous titanylphthalocyanine (low crystallinitytitanylphthalocyanine). In this process, to control such that a longerdiameter of the primary particles of the titanylphthalocyanine crystalafter the crystal conversion is not greater than 0.2 μm is a point ofthe present invention.

Any organic solvent for use in this method can be used if only a desiredcrystal form can be obtained. In particular, a solvent selected from thegroup consisting of tetra hydrofuran, toluene, dichloromethane, carbonbisulfide, o-dichlorobenzene and 1,1,2-trichloroethane is preferablyused. These solvents are preferably used alone, but can also be used incombination or with other solvents.

The present inventors observed in the crystal conversion that theamorphous titanylphthalocyanine (low crystallinitytitanylphthalocyanine) has a primary particle diameter not greater than0.1 μm (almost all the particles have a diameter of from about 0.01 to0.05 μm), and that the crystal grows at the same time. Usually, in sucha crystal conversion, a sufficient time is spent for the crystalconversion such that the materials do not remain and a filteredtitanylphthalocyanine crystal having a desired crystal form is obtainedafter the sufficient crystal conversion. Therefore, the crystal afterthe crystal conversion has large primary particles (about 0.3 to 0.5 μmin diameter) although the material having sufficiently small primaryparticles is used.

When the thus prepared titanylphthalocyanine crystal is dispersed, astrong shear is applied to make the particle size small (not greaterthan about 0.2 μm in diameter). Further, a strong energy is optionallyapplied to pulverize the primary particles. Consequently, a part of theparticles has an undesired crystal form as mentioned above.

On the other hand, the present invention is to obtain atitanylphthalocyanine crystal having a primary particle size as small aspossible by finding out the time when the crystal conversion iscompleted before the crystal hardly grows, i.e., before the amorphoustitanylphthalocyanine particle size becomes greater than about 0.2 μm.The particle size becomes large in proportion to the crystal conversiontime. Therefore, it is essential to enhance the crystal conversionefficiency and complete the conversion in a short time. For thispurpose, there are two important points.

One is to select a suitable crystal conversion solvent as mentionedabove to enhance the crystal conversion efficiency. The other is tostrongly stir the solvent and titanylphthalocyanine water paste asprepared as above such that they sufficiently contact to each other inorder to complete the crystal conversion in a short time. Specifically,stirring methods using strong stirrers such as propeller stirrers andhomogenizers (homomixers) are used to perform the crystal conversion ina short time. These methods can obtain a titanylphthalocyanine crystalsufficiently converted without crystal growth and remaining materials.

In addition, as mentioned above, because the crystal particle size growsin proportion to the crystal conversion time, when a predeterminedreaction (crystal conversion) is completed, it is an effective method tostop the reaction immediately. For example, after the crystal conversionis performed, a large amount of a solvent preventing a crystalconversion is immediately included in the mixture. Suitable solventspreventing a crystal conversion include alcohol solvents, estersolvents, etc. These solvents having an amount of approximately tentimes as much as the crystal conversion solvent can stop the crystalconversion.

The smaller the thus prepared primary particle size, the better for theresultant photoreceptor. However, in consideration of the followingfiltering process to prepare a pigment and dispersion stability thereofin a dispersion liquid, primary particles having too small a sizeoccasionally has an adverse effect. Namely, when the primary particlesize is too small, it takes quite a long time to filter the particles inthe filtering process. In addition, because the primary particles havingtoo small a size totally have a large surface area, probability ofre-agglomeration of the pigment particles increases. Therefore, thepigment particles preferably have a particle size of from about 0.05 to0.2 μm.

Next, the converted titanylphthalocyanine crystal is immediatelyfiltered to be separated from the crystal conversion solvent. A filterhaving a proper size is used for the filtration. The filtration underreduced pressure is most preferably used.

Then, the separated titanylphthalocyanine crystal is optionally heatedand dried. A known drier can be used for heating and drying the crystal.However, a fan drier is preferably used when heating and drying thecrystal are performed in the atmosphere. Further, in order to increasedrying speed and an effect of the present invention, drying underreduced pressure is quite an effective method. Particularly, dryingunder reduced pressure is an effective method for a material which isdissolved by a high temperature or a material the crystal form of whichchanges. In particular, drying in a degree of vacuum which is higherthan 10 mmHg is effective.

The organic pigment having a high capability of generating a photocarrier for use in the present invention typically has quite a highagglutinability. When the crystal is dried as mentioned above afterfiltered and separated, the primary particles agglutinate to formsecondary particles. These secondary particles can be dispersed to theprimary particles with an ordinary disperser. However, the crystal darenot be dried if the crystal conversion solvent and the dispersionsolvent are the same. In that case, a wet cake of thetitanylphthalocyanine crystal after filtered is directly put into thedispersion solvent in which a binder resin is optionally dissolved todisperse the titanylphthalocyanine crystal. This method does not have todisperse the large secondary particles and more distinguishes the effectof the present invention.

The thus prepared titanylphthalocyanine crystal having a primaryparticle diameter not greater than 0.2 μm is effectively used for a CGMfor an electrophotographic photoreceptor. Particularly, thetitanylphthalocyanine crystal having a maximum diffraction peak at aBragg (2 θ) angle of 27.2±0.2° when irradiated with a specific X-ray ofCuKα having a wavelength of 1.542 Å has quite a high photo carriergeneration efficiency. However, as mentioned above, the crystal form isunstable and has a drawback of easily transforming. However, in thepresent invention, the primary

particles which are as small as possible can prepare a dispersion liquidincluding the particles having a small average particle diameter and canmake the crystal form quite stable.

The dispersion liquid is prepared by typical methods using a ball mill,an attritor, a sand mill, a beads mill, an ultrasonic, etc., in whichthe titanylphthalocyanine crystal is optionally dispersed with a binderresin in a proper solvent. The binder resin may be selected forelectrostatic properties of the resultant photoreceptor, and the solventmay be selected for wettability to the pigment and dispersibilitythereof.

Hereinafter, the electrophotographic photoreceptor of the presentinvention will be explained, referring to the drawings.

FIG. 1 is a schematic view illustrating a cross section of an embodimentof the photosensitive layer of the electrophotographic photoreceptor foruse in the present invention, in which a charge generation layer (hereinafter referred to as a CGL) 45 including a CGM as a main component and acharge transport layer (herein after referred to as a CTL) 47 includinga charge transport material (herein after referred to as a CTM) as amain component are formed on an electroconductive substrate 41.

FIG. 2 is a schematic view illustrating a cross section of anotherembodiment of the photosensitive layer of the electrophotographicphotoreceptor for use in the present invention, in which a protectionlayer 49 is layered on a CGL 45 and CTL 47.

Suitable materials for the electroconductive substrate 41 includematerials having a volume resistance not greater than 10¹⁰ Ω·cm.Specific examples of such materials include plastic cylinders, plasticfilms or paper sheets whose surface is deposited or sputtered with ametal such as aluminum, nickel, chromium, nichrome, copper, gold,silver, platinum and the like, or a metal oxide such as tin oxides,indium oxides and the like. In addition, a plate of a metal such asaluminum, aluminum alloys, nickel and stainless steel and a metalcylinder, which is prepared by tubing a metal such as the metalsmentioned above by a method such as impact ironing or direct ironing,and then treating the surface of the tube by cutting, super finishing,polishing and the like treatments, can also be used as the substrate.Further, endless belts of a metal such as nickel and stainless steel,which are disclosed in Japanese Laid-Open Patent Publication No.52-36016, can also be used as the substrate 41.

Among these materials, a cylindrical substrate formed of aluminium whichis easily coated by an anodic oxide coating method can most preferablybe used. The aluminium includes either of pure aluminium and aluminiumbase alloys.

Specifically, aluminium or aluminium base alloys in the thousands, threethousands and six thousands of JIS are most suitable. The anodic oxidecoating method is a method of coating various metals and alloyed metalsin an electrolyte. A film called as alumite formed by the anodic oxidecoating method coating the aluminium or aluminium base alloys in anelectrolyte is most suitable for the photoreceptor for use in thepresent invention. Particularly, when the photoreceptor is used for areverse development (negative and positive development), thephotoreceptor has good capability of preventing point defects such asblack spots and background fouling.

The anodic oxide coating is performed in an acidic solution using achromic acid, a sulfuric acid, an oxalic acid, a phosphoric acid, aboric acid, sulfamic acid, etc. Among these acids, a sulfuric acidsolution is most preferably used. For example, the anodic oxide coatingis usually performed in the conditions of a sulfuric acid concentrationof from 10 to 20%; a liquid temperature of from 5 to 25° C.; a currentdensity of from 1 to 4 A/dm²; a bath voltage of from 5 to 40 V; and aperformance time is 5 to 60 min. However, the conditions are not limitedthereto. Because the thus prepared anodic oxide coated film is porousand highly insulative, the film has a quite an unstable surface.Therefore, as time passes, properties of the anodic oxide coated filmeasily change. In order to avoid this, it is preferable that the anodicoxide coated film is further sealed. The sealing methods include dippingthe anodic oxide coated film in an aqueous solution including nickelfluoride or nickel acetate, or a boiled water and steam sealing. Amongthese methods, the method of dipping the anodic oxide coated film in anaqueous solution including nickel acetate is most preferably used.Following the sealing, the anodic oxide coated film is washed to mainlyremove unnecessary materials such as metallic salts adhered to the filmby the sealing. The excessive materials remaining on a surface of thesubstrate (the anodic oxide coated film) not only have a bad influenceupon quality of a coated film formed thereon but also cause backgroundfouling because low resistance materials typically remain. One timewashing with purified water may be sufficient, but usually the anodicoxide coated film is washed several times. The final cleaning liquid ispreferably as clean as possible (deionized). In addition, one of thetimes is preferably a physical abrasion washing with a contact member.The thus prepared anodic oxide coated film preferably has a thickness offrom about 5 to 15 μm. When the thickness is less than 5 μm, the anodicoxide coated film does not have a sufficient barrier effect. Whengreater than 15 μm, a time constant as an electrode is so large that theresultant photoreceptor occasionally has a residual potential or adeteriorated response.

Besides, substrates on which a coating liquid including a binder resinand an electroconductive powder is coated can also be used as thesubstrate 41. Specific examples of such an electroconductive powderinclude carbon black, acetylene black, powders of metals such asaluminum, nickel, iron, Nichrome, copper, zinc, silver and the like, andmetal oxides such as electroconductive tin oxides, ITO and the like.

Specific examples of the binder resin include known thermoplasticresins, thermosetting resins and photo-crosslinking resins, such aspolystyrene, styrene-acrylonitrile copolymers, styrene-butadienecopolymers, styrene-maleic anhydride copolymers, polyesters, polyvinylchloride, vinyl chloride-vinyl acetate copolymers, polyvinyl acetate,polyvinylidene chloride, polyarylates, phenoxy resins, polycarbonates,cellulose acetate resins, ethyl cellulose resins, polyvinyl butyralresins, polyvinyl formal resins, polyvinyl toluene, poly-N-vinylcarbazole, acrylicresins, silicone resins, epoxy resins, melamine resins, urethane resins,phenolic resins, alkyd resins and the like resins. Such anelectroconductive layer can be formed by coating a coating liquid inwhich an electroconductive powder and a binder resin are dispersed in asolvent such as tetra hydrofuran, dichloromethane, methyl ethyl ketone,toluene and the like solvent, and then drying the coated liquid.

Further, substrates, in which an electroconductive resin film is formedon a surface of a cylindrical substrate using a heat-shrinkable resintube which is made of a combination of a resin such as polyvinylchloride, polypropylene, polyesters, polyvinylidene chloride,polyethylene, chlorinated rubber and fluorine-containing resins, with anelectroconductive material, can also be used as the substrate 41.

Next, a photosensitive layer will be explained.

The CGL 45 is a layer including a titanylphthalocyanine crystal havingan average primary particle diameter not greater than 0.2 μm, which is amain component thereof as a CGM. The titanylphthalocyanine crystalpreferably has at least a maximum diffraction peak at a Bragg (2 θ)angle of 27.2±0.2° when irradiated with a specific X-ray of CuKα havinga wavelength of 1.542 Å. Further, the titanylphthalocyanine crystalhaving main peaks at 9.4°, 9.6° and 24.0°; a minimum diffraction peak at7.3°; and preferably not having peaks at greater than 7.3° and less than9.4°_ is more preferably used. Furthermore, the titanylphthalocyaninecrystal not having a peak at 26.3° is most preferably used.

The CGL 45 can be formed by dispersing the above-mentioned pigment in aproper solvent optionally together with a binder resin using a ballmill, an attritor, a sand mill or a supersonic dispersing machine,coating the coating liquid on an electroconductive substrate and thendrying the coated liquid.

Suitable binder resins optionally used in the CGL 45 include polyamides,polyurethanes, epoxy resins, polyketones, polycarbonates, siliconeresins, acrylic resins, polyvinyl butyral, polyvinyl formal, polyvinylketones, polystyrene, polysulfone, poly-N-vinylcarbazole,polyacrylamide, polyvinyl benzal, polyesters, phenoxy resins, vinylchloride-vinyl acetate copolymers, polyvinyl acetate,

polyphenylene oxide, polyamides, polyvinyl pyridine, cellulose resins,casein, polyvinyl alcohol, polyvinyl pyrrolidone, and the like resins.The content of the binder resin in the CGL 45 is preferably from 0 to500 parts by weight, and preferably from 10 to 300 parts by weight per100 parts by weight of the CGM.

Suitable solvents for use in the coating liquid include isopropanol,acetone, methyl ethyl ketone, cyclohexanone, tetra hydrofuran, dioxane,ethyl cellosolve, ethyl acetate, methyl acetate, dichloromethane,dichloroethane, monochlorobenzene, cyclohexane, toluene, xylene,ligroin, and the like solvents. In particular, ketone type solvents,ester type solvents and ether type solvents are preferably used. Thecoating liquid can be coated by a coating method such as a dip coatingmethod, a spray coating method, a bead coating method, a nozzle coatingmethod, a spinner coating method and a ring coating method. Thethickness of the charge generation layer (35) is preferably from 0.01 to5 μm, and more preferably from 0.1 to 2 μm.

The CTL 47 can be formed by dissolving or dispersing a CTM and a binderresin in a proper solvent, coating the dissolved or dispersed liquid onthe charge generation layer and drying the coated liquid. Additives suchas plasticizers, leveling agents and antioxidants may be included in theCTL if desired.

The CTMs are classified into positive-hole transport materials andelectron transport materials. Specific examples of the electrontransport materials include electron accepting materials such aschloranil, bromanil, tetracyanoethylene, tetracyanoquinodimethane,2,4,7-trinitro-9-fluorenon, 2,4,5,7-tetranitro-9-fluorenon,2,4,5,7-tetanitroxanthone, 2,4,8-trinitrothioxanthone,2,6,8-trinitro-4H-indeno[1,2-b]thiophene-4-one,1,3,7-trinitrodibenzothiphene-5,5-dioxide, benzoquinone derivatives andthe like.

Specific examples of the positive-hole transport materials include knownmaterials such as poly-N-carbazole and its derivatives,poly-γ-carbazolylethylglutamate and its derivatives, pyrene-formaldehydecondensation products and their derivatives, polyvinyl pyrene, polyvinylphenanthrene, polysilane, oxazole derivatives, oxadiazole derivatives,imidazole derivatives, monoarylamines, diarylamines, triarylamines,stilbene derivatives, α-phenyl stilbene derivatives, benzidinederivatives, diarylmethane derivatives, triarylmethane derivatives,9-styrylanthracene derivatives, pyrazoline derivatives, divinyl benzenederivatives, hydrazone derivatives, indene derivatives, butadienederivatives, pyrene derivatives, bisstilbene derivatives, enaminederivatives, etc. These CTMs can be used alone or in combination.

Specific examples of the binder resin include thermoplastic resins orthermosetting resins such as polystyrene, styrene-acrylonitrilecopolymers, styrene-butadiene copolymers, styrene-maleic anhydridecopolymers, polyesters, polyvinyl chloride, vinyl chloride-vinyl acetatecopolymers, polyvinyl acetate, polyvinylidene chloride, polyarylates,phenoxy resins, polycarbonates, cellulose acetate resins, ethylcellulose resins, polyvinyl butyral resins, polyvinyl formal resins,polyvinyl toluene, poly-N-vinyl carbazole, acrylic resins, siliconeresins, epoxy resins, melamine resins, urethane resins, phenolic resinsand alkyd resins.

The content of the CTM is preferably from 20 to 300 parts by weight, andmore preferably from 40 to 150 parts by weight per 100 parts by weightof the binder resin. The CTL preferably has a thickness of from about 5to 100 μm. Suitable solvents for use in the coating liquid include tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene,dichloroethane, cyclohexanone, methyl ethyl ketone, acetone and the likesolvents.

The CTL 47 preferably includes a polymer CTM, which has both a binderresin function and a charge transport function, because the resultantCTL has good abrasion resistance. Suitable charge transport polymermaterials include known polymer CTMs. Among these materials,polycarbonate resins having a triarylamine structure in their main chainand/or side chain are preferably used. In particular, polymer CTMshaving the following formulae (I) to (X) are preferably used:

wherein, R₁, R₂ and R₃ independently represent a substituted orunsubstituted alkyl group, or a halogen atom; R₄ represents a hydrogenatom, or a substituted or unsubstituted alkyl group; R₅, and R₆independently represent a substituted or unsubstituted aryl group; o, pand q independently represent 0 or an integer of from 1 to 4; k is anumber of from 0.1 to 1.0 and j is a number of from 0 to 0.9; nrepresents a repeating number and is an integer of from 5 to 5000; and Xrepresents a divalent aliphatic group, a divalent alicyclic group or adivalent group having the following formula:

wherein, R₁₀₁ and R₁₀₂ independently represent a substituted orunsubstituted alkyl group, an aromatic ring group or a halogen atom; 1and m represent 0 or an integer of from 1 to 4; and Y represents adirect bonding, a linear alkylene group, a branched alkylene group, acyclic alkylene group, —O—, —S—, —SO—, —SO2-, —CO—, —CO—O—Z—O—CO— (Zrepresents a divalent aliphatic group), or a group having the followingformula:

wherein, a is an integer of from 1 to 20; b is an integer of from 1 to2000; and R₁₀₃ and R₁₀₄ independently represent a substituted orunsubstituted alkyl group, or a substituted or unsubstituted aryl group,and wherein R₁₀₁, R₁₀₂, R₁₀₃ and R₁₀₄ may be the same or different fromthe others;

wherein, R₇ and R₈ represent a substituted or unsubstituted aryl group;Ar₁, Ar₂ and Ar₃ independently represent an arylene group; and X, k, jand n are same in formula (I);

wherein, R₉ and R₁₀ represent a substituted or unsubstituted aryl group;Ar₄, Ar₅ and Ar₆ independently represent an arylene group; and X, k, jand n are same in formula (I);

wherein, R₁₁ and R₁₂ represent a substituted or unsubstituted arylgroup; Ar₇, Ar₈ and Ar₉ independently represent an arylene group; p isan integer of from 1 to 5; and X, k, j and n are same in formula (I);

wherein, R₁₃ and R₁₄ represent a substituted or unsubstituted arylgroup; Ar₁₀, Ar₁₁ and Ar₁₂ independently represent an arylene group; X₁and X₂ represent a substituted or unsubstituted ethylene group, or asubstituted or unsubstituted vinylene group; and X, k, j and n are samein formula (I);

wherein, R₁₅, R₁₆, R₁₇ and R₁₈ represent a substituted or unsubstitutedaryl group; Ar₁₃, Ar₁₄, Ar₁₅ and Ar₁₆ independently represent an arylenegroup; Y₁, Y₂ and Y₃ independently represent a direct bonding, asubstituted or unsubstituted alkylene group, a substituted orunsubstituted cycloalkylene group, a substituted or unsubstitutedalkylene ether group, an oxygen atom, a sulfur atom, or a vinylenegroup; and X, k, j and n are same in formula (I);

wherein, R₁₉ and R₂₀ represent a hydrogen atom, or substituted orunsubstituted aryl group, and R₁₉ and R₂₀ may form a ring; Ar₁₇, Ar₁₈and Ar₁₉ independently represent an arylene group; and X, k, j and n aresame in formula (I);

wherein, R₂₁ represents a substituted or unsubstituted aryl group; Ar₂₀,Ar₂₁, Ar₂₂ and Ar₂₃ independently represent an arylene group; and X, k,j and n are same in formula (I);

wherein, R₂₂, R₂₃, R₂₄ and R₂₅ represent a substituted or unsubstitutedaryl group; Ar₂₄, Ar₂₅, Ar₂₆, Ar₂₇ and Ar₂₈ independently represent anarylene group; and X, k, j and n are same in formula (I);

wherein, R₂₆ and R₂₇ independently represent a substituted orunsubstituted aryl group; Ar₂₉, Ar₃₀ and Ar₃₁ independently represent anarylene group; and X, k, j and n are same in formula (I).

In addition, other than the above-mentioned polymer CTMs, the polymerCTMs for use in the CTL include polymers finally having atwo-dimensional or three-dimensional crosslinking structure, which is amonomer or an oligomer having an electron-releasing group when the CTLis formed and hardened or crosslinked after the CTL is formed.

The CTL constituted of these polymers having an electron-releasing groupor a crosslinking structure has a good abrasion resistance. Usually, inan electrophotographic process, charge potential (unexposed partspotential) is fixed, and when a surface of a photoreceptor is abradeddue to repeated use, electric intensity increases in proportion to theabrasion. Accompanied with an increase of the electric intensity,occurrence of background fouling increases, and therefore, aphotoreceptor having a high abrasion resistance has an advantage againstthe background fouling. The CTL constituted of these polymers having anelectron-releasing group is easily coated because the CTL itself is apolymer compound. In addition, the CTL has a good chargetransportability because of having a higher-density charge transportportion than a CTL constituted of a polymer in which alow-molecular-weight compound is dispersed. Therefore, a high-speedresponse can be expected from a photoreceptor having a CTL using apolymer CTM.

Other polymers having an electron-releasing group include copolymers ofknown monomers, block polymers, graft polymers, star polymers andcrosslinked polymers having an electron-releasing group disclosed inJapanese Laid-Open Patent Publications Nos. 3-109406, 2000-206723 and2001-34001.

The CTL in the present invention may include additives such asplasticizers and leveling agents. Specific examples of the plasticizersinclude known plasticizers, which are used for plasticizing resins, suchas dibutyl phthalate and dioctyl phthalate. The addition quantity of theplasticizer is 0 to 30% by weight of the binder resin. Specific examplesof the leveling agents include silicone oils such as dimethyl siliconeoil and methyl phenyl silicone oil; polymers or oligomers including aperfluoroalkyl group in their side chain; and the like. The additionquantity of the leveling agents is 0 to 1% by weight of the binderresin.

Suitable binder resins include the resins mentioned above for use in theCTL 47. The resins mentioned above for use in the CGL 45 can be added asa binder resin. In addition, the charge transport polymer materialsmentioned above can also be used as a binder resin. The content of thecharge generation material is preferably from 5 to 40 parts by weightper 100 parts by weight of the binder resin. The content of the chargetransport material is preferably from 0 to 190 parts by weight, and morepreferably from 50 to 150 parts by weight per 100 parts by weight of thebinder resin. A single-layered photosensitive layer can be formed bycoating a coating liquid in which a charge generation material and abinder, and optionally a charge transport material, are dissolved ordispersed in a solvent such as tetra hydrofuran, dioxane, dichloroethaneand cyclohexane by a coating method such as a dip coating, a spraycoating and a bead coating method. The thickness of the photosensitivelayer is preferably from about 5 to 100 μm.

In the photoreceptor of the present invention, an undercoat layer may beformed between the electroconductive substrate 41 and the photosensitivelayer. The undercoat layer includes a resin as a main component. Since aphotosensitive layer is typically formed on the undercoat layer bycoating a liquid including an organic solvent, the resin in theundercoat layer preferably has good resistance to general organicsolvents. Specific examples of such resins include water-soluble resinssuch as polyvinyl alcohol resins, casein and polyacrylic acid sodiumsalts; alcohol soluble resins such as nylon copolymers andmethoxymethylated nylon resins; and thermosetting resins capable offorming a three-dimensional

network such as polyurethane resins, melamine resins, alkyl-melamineresins and epoxy resins. The undercoat layer may include a fine powderof metal oxides such as titanium oxide, silica, alumina, zirconiumoxide, tin oxide and indium oxide to prevent occurrence of moiré in theresultant images and to decrease residual potential of thephotoreceptor.

The undercoat layer can also be formed by coating a coating liquid usinga proper solvent and a proper coating method similarly to those for usein formation of the photosensitive layer mentioned above. The undercoatlayer may be formed using a silane coupling agent, titanium couplingagent or a chromium coupling agent. In addition, a layer of aluminumoxide which is formed by an anodic oxidation method and a layer

of an organic compound such as polyparaxylylene (parylene) or aninorganic compound such as SiO, SnO₂, TiO₂, ITO or CeO₂ which is formedby a vacuum evaporation method is also preferably used as the undercoatlayer. The thickness of the undercoat layer is preferably 0 to 5 μm.

In the photoreceptor of the present invention, a protection layer 49 isoptionally formed overlying the photosensitive layer. Suitable materialsfor use in the

protection layer 49 include ABS resins, ACS resins, olefin-vinyl monomercopolymers, chlorinated polyethers, aryl resins, phenolic resins,polyacetal, polyamides, polyamideimide, polyacrylates, polyarylsulfone,polybutylene, polybutylene terephthalate, polycarbonate, polyarylate,polyethersulfone, polyethylene, polyethylene terephthalate, polyimides,acrylic resins, polymethylpentene, polypropylene, polyphenyleneoxide,polysulfone, polystyrene, AS resins, butadiene-styrene copolymers,polyurethane, polyvinyl chloride, polyvinylidene chloride, epoxy resins,etc. Among these resins, polycarbonate resins or polyarylate resins arepreferably used.

Other than these resins, the protection layer 49 can includefluorocarbon resins such as polytetrafluoroethylene, silicone resins andmaterials constituted of these resins in which inorganic fillers such astitanium oxide, tin oxide, kalium titanate and silica or organic fillersare dispersed for the purpose of improving abrasion resistance thereof.

Specific examples of the organic fillers include powders of fluorocarbonresins such as polytetrafluoroethylene, silicone resin powders anda-carbon powders. Specific examples of the inorganic fillers includepowders of metals such as copper, tin, aluminum and indium; metal oxidessuch as silica, tin oxide, zinc oxide, titanium oxide, indium oxide,antimony oxide, bismuth oxide, tin oxide doped with antimony, indiumoxide doped with tin and potassium titanate. Among these fillers,inorganic fillers are preferably used in view of their hardness. Inparticular, silica, titanium oxide and alumina are preferably used.Further, α-alumina having a hexagonal close-packed structure is morepreferably used.

Although concentration of the filler in the protection layer depends ona kind of the filler and electrophotographic process conditions usingthe resultant photoreceptor, the filler preferably has a content of from5 to 50% by weight, and more preferably from 10 to 30% by weight basedon total weight of solid contents in most surface of the protectionlayer.

In addition, the filler preferably has a volume-average particlediameter of from 0.1 to 2 μm, and more preferably from 0.3 to 1 μm. Whenthe average particle diameter is too small, the protection layer doesnot have sufficient abrasion resistance. When too large, the protectionlayer has a poor surface smoothness and cannot be formed in some cases.

The average particle diameter of the filler in the present invention isa volume-average particle diameter thereof unless otherwise specified,and measured by an ultra centrifugal automaticparticle-size-distribution measurer CAPA-700 from Horiba, Ltd. This isdetermined as a particle diameter which is equivalent to 50% ofcumulative distribution (Median value). Further, it is important that astandard deviation of each particle measured at the same time is notgreater than 1 μm. When the standard deviation is greater than 1 μm, theparticle diameter distribution is so wide that the effect of the presentinvention is not occasionally exerted.

pH of the filler largely affects resolution of the resultant image anddispersibility of the filler. It is considered that one of the reasonsis that a hydrochloric acid and the like acid remain in the filler,particularly in the metal oxide. When the remaining amount of the acidsis large, production of the resultant blurred images cannot be avoided,and dispersibility of the filler is occasionally influenced therebydepending on the remaining amount.

The other reason is a difference of chargeability of the filler,particularly the metal oxide. Usually, particles dispersed in a liquidare positively or negatively charged, and ions having a contrariouscharge gather to keep the particles neutral. Then, an electric doublelayer is formed to stabilize the dispersibility of the particles. As thelayer leave from the particles, the potential (zeta potential) graduallydecreases and a potential of an electrically neutral area sufficientlyapart from the particles becomes zero. Therefore, when an absolute valueof the zeta potential increases, a force of repulsion of the particlesincreases and stability thereof increases. As the zeta potential closesto zero, the particles tend to agglutinate and become unstable.

On the other hand, according to pH of the dispersion liquid, the zetapotential largely fluctuates. The potential becomes zero at a certain pHand the dispersion liquid has an isoelectric point. Therefore, theparticles are kept away from the isoelectric point as far as possible tostabilize the dispersion liquid.

In the present invention, the filler preferably has a pH at least notless 5 at the isoelectric point to prevent the resultant blurred images,and the effect increases when the filler is more basic. Dispersibilityand stability of the basic filler having a high pH improves when thedispersion liquid is acidic because the zeta potential more increases.

pH values of the filler in the present invention are values from thezeta potential to isoelectric point, and the zeta potential is measuredby a laser zeta electrometer from Otsuka Electronics Co., Ltd.

In order to prevent occurrence of blurred images, fillers having arelatively high specific resistance not less than 10¹⁰ Ω·cm arepreferably used in the protection layer. In addition, fillers having apH not less than 5 or a dielectric constant not less than 5 arepreferably used. These fillers can be used alone or in combination. Forexample, a combination of two or more kinds of a filler having a pH notless than 5 and a filler having a pH not greater than 5; or acombination of two or more kinds of a filler having a dielectricconstant not less than 5 and a filler having a dielectric constant notgreater than 5 can be used. Among these fillers, α-form alumina, whichhas a hexagonal close-packed structure, is preferably used to improveabrasion resistance of the resultant protection layer and to prevent theblurred image problem, because the alumina has high insulation property,heat stability and good abrasion resistance.

Resistivity of the filler for use in the present invention is determinedas follows. Because a powder like the filler has a different resistivityaccording to the filling factor, the resistivity has to be measuredunder fixed conditions. In the present invention, a measurer having anequivalent structure to a measurer disclosed in each FIG. 1 of JapaneseLaid-Open Patent Publications Nos. 5-94049 and 5-113688 is used tomeasure the resistivity of the filler. The measurer has an electrodearea of 4.0 cm². An amount of a sample is controlled such that adistance between the electrodes is 4 mm by applying a load of 4 kg toone of the electrodes for 1 min before measured. The measurement isperformed on loaded status of the upper electrode having a weight of 1kg with an applied voltage of 100 V. A scope not less than 10⁶ Ω·cm ismeasure by HIGH RESISTANCE METER from Yokogawa Hewlett Packard Ltd. anda scope less than that is measure by Digital Multimeter from Fluke Corp.

Dielectric constant of the filler is measured as follows. A cell whichis similar to that used in the measurement of resistivity is used, andcapacitance is measured after a load is applied thereto to measure thedielectric constant. The capacitance is measure by a dielectric lossmeasurer from Ando Electric Co., Ltd.

Further, the fillers are preferably treated with at least one surfacetreating agent to improve the dispersibility thereof. Deterioration ofdispersibility of a filler included in the protection layer causes notonly increase of residual potential but also decrease of transparency ofthe protection layer, generation of coating deficiencies anddeterioration of abrasion resistance. Therefore, a photoreceptor havinggood durability and capable of producing good images cannot be provided.Suitable surface treating agents include known surface treating agents,but surface treating agents which can maintain the insulating propertiesof the filler in the protection layer are preferably used. Specificexamples of such surface treating agents include titanate couplingagents, aluminum coupling agents, zircoaluminate coupling agents, higherfatty acids, and combinations of these agents with silane couplingagents; and Al₂O₃, TiO₂, ZrO₂, silicones, aluminum stearate, and theirmixtures. These are preferably used because of being capable ofimparting good dispersibility to fillers and preventing blurred images.When silane coupling agents are used, the blurred image problem tends tooccur. However, when used in combination with the surface treatingagents mentioned above, there is a case in which the problem can beavoided. The content of a surface treating agent in a coated filler,which depends on the primary particle diameter of the filler, is from 3to 30% by weight, and more preferably from 5 to 20% by weight. When thecontent is too low, good dispersibility cannot be obtained. To thecontrary, when the content is too high, residual potential seriouslyincreases. These fillers can be used alone or in combination. An amountof the surface treatment of the filler is determined by a weight ratioof the surface treating agents to an amount of the filler.

The filler materials can be dispersed by a proper disperser. Inaddition, it is preferable that the filler is dispersed to primaryparticles and has less agglutinated bodies in respect of transmittanceof the protection layer.

The protection layer 49 may include a CTM to decrease residual potentialand to improve the response of the resultant photoreceptor. The CTMsmentioned above for use in the CTL can be used. When alow-molecular-weight CTM is used in the protection layer, theconcentration gradient of the low-molecular-weight CTM may be formedtherein. In this case, it is preferable that the concentration of theCTM at the surface of the protection layer is lower than that at thebottom thereof to improve the abrasion resistance of the resultantphotoreceptor. The concentration is a weight ratio of thelow-molecular-weight CTM to a total weight of the all the materialsincluded in the protection layer. The concentration gradient means sucha gradient as lowers the concentration of the CTM at the surface ofprotection layer.

In addition, using a charge transport polymer material is quiteadvantageous to increase durability of the resultant photoreceptor. Whenthe protection layer includes only the charge transport polymer materialbesides the filler, the resultant photoreceptor has not only highmechanical abrasion resistance but also high chemical stability. Thecharge transport polymer material has less chemical reactivity than thelow-molecular-weight CTM and has high resistance against an oxide gasgenerated by a charger and a sputtering effect due to a dischargethereby. When a photoreceptor has a surface layer having a high abrasionresistance such as a protection layer, blurred image problems due to arepeated use frequently occur. It is considered to that this is due toadherence of the oxide gas and a low-resistant material to a surface ofthe photoreceptor. However, the protection layer including only thefiller and the charge transport polymer material decreases the adherencesite and exerts a high effect on the blurred image.

The protection layer is formed by a conventional coating method. Theprotection layer preferably has a thickness of from 0.1 to 10 μm. Inaddition, a protection layer formed by a vacuum thin film forming methodusing known materials such as a-C and a-SiC can be used.

As mentioned above, a photosensitive layer (CTL) including a polymer CTMor a protection layer formed on a surface of a photoreceptor not onlyincreases durability (abrasion resistance) of the photoreceptor but alsoexerts a new effect when used in a tandem-type full-color image formingapparatus, which is not available in a monochrome image formingapparatus.

In the full-color image forming apparatus, various modes of images areinput and formulaic images are also input, e.g., proof marks in Japanesedocuments. Such proof marks are usually located at the edges of theimages and the colors are limited. Further, a tandem-type full-colorimage forming apparatus prevails and a printing speed thereof improves,and many business documents having, e.g., a company logo are produced.In such a case, a specific part is repeatedly printed and an uneven useof the photoreceptor becomes large. When random images are alwayswritten in a photoreceptor, image writing, development and transfer areperformed thereon on average. When images are repeatedly written in aspecific part of the photoreceptor or only specific image formingelements

thereof are used, a balance of durability thereof is lost. When aphotoreceptor not having so (physically, chemically and mechanically)durable a surface in such conditions, the balance loss becomes large andcauses image problems. On the other hand, a photoreceptor having a highdurability has less local loss and produces less defective images.

In the present invention, an intermediate layer can be formed betweenthe photosensitive layer and the protection layer. The intermediatelayer includes a resin as a main component. Specific examples of theresin include polyamides, alcohol soluble nylons, water-solublepolyvinyl butyral, polyvinyl butyral, polyvinyl alcohol, etc. Theintermediate layer can be formed by one of the above-mentioned knowncoating methods. The thickness of the intermediate layer is preferablyfrom 0.05 to 2 μm.

Hereinafter, the electrophotographic method and electrophotographicapparatus of the present invention will be explained referring todrawings.

FIG. 3 is a schematic view illustrating a cross section of an embodimentof the electrophotographic apparatus for explaining theelectrophotographic process of the present invention, and modifiedembodiments are included in the present invention.

In FIG. 3, a photoreceptor 21 is formed of a CGL including atitanylphthalocyanine crystal having an average primary particlediameter not greater than 0.2 μm and a CTL on an electroconductivesubstrate. Known means such as corotrons, scorotrons, solid statechargers and charging rollers are used for a charging member 23, apre-transfer charger 27, transfer charger 30, a separation charger 31and a pre-cleaning charger 33. The charging member preferably contactsthe photoreceptor or is located closely thereto. It is preferable that aDC voltage overlapped with an AC voltage is applied to the photoreceptorto reduce uneven charging. Particularly, in the tandem-type full-colorimage forming apparatus, the uneven charging causes a large problem ofdeterioration of color balance (color reproducibility) in addition touneven density of halftone images occurred in a monochrome image formingapparatus. Overlapping an AC voltage with a DC voltage largely improvesthe problem. However, when properties of the AC voltage such asfrequencies and peak voltages are too large, a hazard to thephotoreceptor becomes large, which occasionally

accelerates deterioration of the photoreceptor. Therefore, the ACvoltage overlapping has to be a minimum required.

The contact charging member is a member contacting its surface to thatof the photoreceptor, and has the shape of a charging roller, chargingblade and a charging brush. Particularly, the charging rollers andbrushes are preferably used.

The charging member located closely to the photoreceptor is anon-contact member such that there is a gap of not greater than 200 μmbetween the surfaces of the photoreceptor and the charging member. Whenthe gap is too large, the photoreceptor is unstably charged. When toosmall, a residual toner on the photoreceptor contaminates the surface ofthe charging member. Therefore, the gap is preferably from 10 to 200 μm,and more preferably from 10 to 100 μm. According to a length of the gap,known charge wire type chargers such as corotrons and scorotrons and thecontact charging members such as charging rollers, charging brushes andcharging blades are separately used.

The charging member located closely to a photoreceptor for use in thepresent invention may have any shape provided that the gap from thephotoreceptor can be properly controlled. For example, rotation axes ofthe photoreceptor and charging member may mechanically be fixed suchthat there is a proper gap. Simple methods of stably maintaining the gapinclude a method of using a charging roller having a gap forming memberat both non-image forming ends thereof, which only contact the surfaceof photoreceptor such that the image forming area thereof does notcontact the member, or a method of locating the gap forming members atboth non-image forming ends of the photoreceptor, which only contact thesurface of the charging member such that the image forming area does notcontact the charging member. Particularly, methods disclosed in JapaneseLaid-Open Patent Publications Nos. 2002-148904 and 2002-148905 arepreferably used. An embodiment of the charger located closely to thephotoreceptor, which has a gap forming member is shown in FIG. 4.

As a transferer, the above-mentioned chargers can typically be used, andas FIG. 3 shows, a combination of the transfer charger 30 and theseparation charger 31 is preferably used.

Suitable light sources for use in an irradiator 25 include laser diodes(LDs) and light emitting diodes (LEDs). Suitable light sources for usein a discharging lamp 22 include general light-emitting materials suchas fluorescent lamps, tungsten lamps, halogen lamps, mercury lamps,sodium lamps, LEDs, LDs, light sources using electroluminescence (EL),etc. In addition, in order to obtain light having a desired wave lengthrange, filters such as sharp-cut filters, band pass filters,near-infrared cutting filters, dichroic filters, interference filters,color temperature converting filters, etc. can be used.

The above-mentioned light sources can be used for not only the processillustrated in FIG. 3, but also other processes such as a transferprocess, a discharging process, a cleaning process, a pre-exposureprocess including light irradiation to the photoreceptor.

When a toner image formed on the photoreceptor 21 by a developing unit26 is transferred onto a transfer sheet 29, all of the toner image isnot transferred thereto, and a residual toner remains on the surface ofthe photoreceptor 21. The residual toner is removed from thephotoreceptor by the fur brush 34 and the cleaning blade 35. Theresidual toner

remaining on the photoreceptor 21 can be removed by only a cleaningbrush. Suitable cleaning brushes include known cleaning brushes such asfur brushes and mag-fur brushes.

When the photoreceptor positively (or negatively) charged is exposed toimagewise light, an electrostatic latent image having a positive (ornegative) charge is formed on the photoreceptor. When the latent imagehaving a positive (or negative) charge is developed with a toner havinga negative (or positive) charge, a positive image can be obtained. Incontrast, when the latent image having a positive (negative) charge isdeveloped with a toner having a positive (negative) charge, a negativeimage can be obtained.

As the developing method, known developing methods can be used. Inaddition, as the discharging methods, known discharging methods can alsobe used.

FIG. 5 is a schematic view illustrating another embodiment of theelectrophotographic process of the present invention. A photoreceptor 61is formed of a CGL including a titanylphthalocyanine crystal having anaverage primary particle diameter not greater than 0.2 μm and a CTL onan electroconductive substrate. The photoreceptor is rotated by rollers62 a and 62 b. Charging using a charger 63, imagewise exposure using animagewise light irradiator 64, developing using an image developer (notshown), transferring using a transfer charger 65, pre-cleaning using alight source 66, cleaning using a cleaning brush 67 and dischargingusing a discharging light source 68 are repeatedly performed. In FIG. 5,the pre-cleaning light irradiation is performed from the side of thesubstrate of the photoreceptor 61. In this case, the substrate has to belight-transmissive. LDs or LEDs are preferably used for the imagewiselight irradiator 64.

The image forming process of the present invention is not limited to theembodiments as shown in FIGS. 3 and 5. For example, although thepre-cleaning light irradiation is performed from the substrate side inFIG. 5, the pre-cleaning light irradiation can be performed from thephotosensitive layer side of the photoreceptor. In addition, the lightirradiation in the imagewise light irradiation process and thedischarging process may be performed from the substrate side of thephotoreceptor

As light irradiation processes, the imagewise irradiation, pre-cleaningirradiation and discharging light irradiation are illustrated. Inaddition, a pre-transfer light irradiation and a preliminary lightirradiation before the imagewise light irradiation, and other knownlight irradiation processes may also be performed on the photoreceptor.

The above-mentioned image forming units may be fixedly set in a copier,a facsimile or a printer. However, the image forming units may be settherein as a process cartridge. The process cartridge means an imageforming unit (or device) including at least a photoreceptor, and one ofa charger, an imagewise light irradiator, an image developer, an imagetransferer, a cleaner and a discharger. Various process cartridges canbe used in the present invention. FIG. 6 illustrates an embodiment ofthe process cartridge. A photoreceptor 76 is formed of a CGL including atitanylphthalocyanine crystal having an average primary particlediameter not greater than 0.2 μm and a CTL on an electroconductivesubstrate.

FIG. 7 is a schematic view illustrating an embodiment of the tandem-typefull-color image forming apparatus of the present invention, and thefollowing modified embodiment is included in the present invention.

In FIG. 7, numerals 1C, 1M, 1Y and 1K represent drum-shapedphotoreceptors, and rotated in the direction indicated by an arrow.Around the photoreceptors, chargers 2C, 2M, 2Y and 2K; image developers4C, 4M, 4Y and 4 k; and cleaners 5C, 5M, 5Y and 5K are arranged in arotation order thereof. The chargers 2C, 2M, 2Y and 2K uniformly chargesurfaces of the photoreceptors. Laser beams 3C, 3M, 3Y and 3K fromirradiators (not shown) irradiate the surfaces of the photoreceptorsbetween the chargers 2C, 2M, 2Y and 2K and image developers 4C, 4M, 4Yand 4 k to form electrostatic latent images on the surfaces of thephotoreceptors 1C, 1M, 1Y and 1K. Four image forming units 6C, 6M, 6Yand 6K including the photoreceptors 1C, 1M, 1Y and 1K are arranged alonga transfer feeding belt 10 feeding a transfer material. The transferfeeding belt 10 contacts the photoreceptors 1C, 1M, 1Y and 1K betweenthe image developers 4C, 4M, 4Y and 4 k and cleaners 5C, 5M, 5Y and 5Kof the image forming units 6C, 6M, 6Y and 6K. Transfer brushes 11 c,11M, 11Y and 11K are arranged on a backside of the transfer feeding belt10, which is an opposite side to the photoreceptors, to apply a transferbias to the transfer feeding belt 10. The image forming units 6C, 6M, 6Yand 6K just handle different color toners respectively, and have thesame structures.

In the full-color electrophotographic apparatus in FIG. 7, images areformed as follows. First, in the image forming units 6C, 6M, 6Y and 6K,the photoreceptors 1C, 1M, 1Y and 1K are charged by the chargers 2C, 2M,2Y and 2K rotating in the same direction of the photoreceptors. Next,the laser beams 3C, 3M, 3Y and 3K from irradiators (not shown) irradiatethe surfaces of the photoreceptors to form electrostatic latent imageshaving different colors respectively thereon. Then, the image developers4C, 4M, 4Y and 4 k develop the electrostatic latent images to form tonerimages. The image developers 4C, 4M, 4Y and 4 k develop theelectrostatic latent images with toners having a cyan color C, a magentacolor M, a yellow color Y and a black color K respectively. The colortoner images respectively formed on the photoreceptors 1C, 1M, 1Y and 1Kare overlaid on a transfer sheet 7. The transfer sheet 7 is fed by apaper feeding roller 8 from a tray and stopped once by a pair of resistrollers 9, and fed onto the transfer feeding belt 10 in timing withformation of the toner images on the photoreceptors. The transfer sheet7 borne by the transfer feeding belt 10 is transferred to the contact(transfer) position of each photoreceptor 1C, 1M, 1Y and 1K, where eachcolor toner image is transferred onto the transfer sheet 7. The tonerimages on the photoreceptors are transferred to the transfer sheet 7 byan electric field formed with a potential difference between thetransfer bias applied by the transfer brushes 11 c, 11M, 11Y and 11K andthe photoreceptors 1C, 1M, 1Y and 1K. The transfer sheet 7 having passedthe four transfer positions and bearing the four color toner imagesoverlaid thereon is fed to a fixer 12 fixing the toner images on thetransfer sheet. The transfer sheet 7 on which the toner images are fixedis fed onto a sheet receiver (not shown). Residual toners remaining onthe photoreceptors 1C, 1M, 1Y and 1K, which were not transferred on thetransfer sheet at the transfer position are collected by the cleaners5C, 5M, 5Y and 5K. In an embodiment in FIG. 7, the image forming-unitsare lined in order of C, M, Y and K from an upstream to a downstream offeeding direction of the transfer sheet. However, the order is notlimited thereto and the color orders are optional. When only a blackimage is produced, the image forming units 6C, 6M and 6Y except for 6Kcan be stopped in the apparatus of the present invention. In FIG. 7, thecharger contacts the photoreceptor, however, a gap there between of from10 to 200 μm can decrease an abrasion amount thereof and toner filmingover the charger.

The above-mentioned image forming units may be fixedly set in a copier,a facsimile or a printer. However, the image forming units may be settherein as a process cartridge. The process cartridge means an imageforming unit (or device) including at least a photoreceptor, and one ofa charger, an imagewise light irradiator, an image developer, an imagetransferer, a cleaner and a discharger.

Having generally described this invention, further understanding can beobtained by reference to certain specific examples which are providedherein for the purpose of illustration only and are not intended to belimiting. In the descriptions in the following examples, the numbersrepresent weight ratios in parts, unless otherwise specified.

EXAMPLES Example 1

292 parts of 1,3-diiminoisoindoline and 1,800 parts of sulfolane weremixed, and 204 parts of titaniumtetrabutoxide were dropped into themixture under a nitrogen gas stream. The mixture was gradually heateduntil the mixture had a temperature of 180° C. and stirred for 5 hrswhile the reaction temperature was maintained from 170 to 180° C. Afterthe mixture was cooled, a precipitated material (powder) was filteredand washed with chloroform until the powder became blue. Next, thepowder was washed with methanol for several times, and further washedwith hot water having a temperature of 80° C. for several times toprepare a crude titanylphthalocyanine pigment.

60 parts of the crude titanylphthalocyanine pigment was mixed in 1,000parts of sulfonic acid having a concentration of 96% and stirred thereinat a temperature of from 3 to 5° C. to dissolve the pigment therein, andthe mixture was filtered to prepare a sulfonic acid solution. Thesulfonic acid solution was dropped in 35,000 parts of iced water whilestirred, and a precipitated crystal was filtered. Then, the crystal wasrepeatedly washed with water until the water became neutral to prepare awater paste of a titanylphthalocyanine pigment.

1,500 parts of tetra hydrofuran were included in the water paste and themixture was strongly stirred by a homomixer (MARK II f model from KENISCO., LTD.) at 2,000 rpm at a room temperature for 20 min until a colorof the water paste changed from navy blue to pale blue. Then, the stirwas stopped and the mixture was immediately filtered at a reducedpressure. A crystal after the filtration was washed with tetrahydrofuran to prepare 98 parts of a wet cake of the pigment. The wetcake of the pigment was dried at 70° C. under a reduced pressure (5 mmHg) for 2 days to prepare 78 parts of a titanylphthalocyanine crystal.This is a Pigment 1.

Example 2

The procedures of preparation for the titanylphthalocyanine crystal inExample 1 were repeated except for changing the crystal conversionsolvent from the tetra hydrofuran to toluene to prepare atitanylphthalocyanine crystal. This is a Pigment 2.

Example 3

The procedures of preparation for the titanylphthalocyanine crystal inExample 1 were repeated except for changing the crystal conversionsolvent from the tetra hydrofuran to dichloromethane to prepare atitanylphthalocyanine crystal. This is a Pigment 3.

Comparative Example 1

The procedures of preparation for the titanylphthalocyanine crystal inExample 1 were repeated except for changing the crystal conversionsolvent from the tetra hydrofuran to 2-butanone to prepare atitanylphthalocyanine crystal. This is a Pigment 4.

Comparative Example 2

The procedures of preparation for the titanylphthalocyanine crystal inExample 1 were repeated except that the crystal conversion time by thetetra hydrofuran was 4 hrs in accordance with the Synthesis Example 1disclosed in Japanese Laid-Open Patent Publication No. 2001-19871 toprepare a titanylphthalocyanine crystal. This is a Pigment 5.

Comparative Example 3

The procedures of preparation for the titanylphthalocyanine crystal inExample 1 were repeated except that the crystal conversion time by thetetra hydrofuran was 0.4 hrs in accordance with the Synthesis Example 1disclosed in Japanese Laid-Open Patent Publication No. 2001-19871, andfurther the mixture was left for a day and filtered to prepare atitanylphthalocyanine crystal. This is a Pigment 6.

A part of the water paste prepared in Example 1 was diluted with ionexchange water so as to have about 1% by weight. A surface of thediluted water paste was scooped with a copper net subjected to anelectroconductive treatment to observe particle sizes of thetitanylphthalocyanine with a TEM (H-9000NAR from Hitachi, Ltd.) of75,000 magnifications. The average particle size was determined asfollows.

The observed TEM image was photographed to randomly select 30titanylphthalocyanine particles having a shape close to a needle, and amajor axis of each particle was measured. An arithmetic average of themajor axes of the 30 particles was determined as the average particlesize.

The average particle size measured by this method in the water paste inExample 1 was 0.06 μm.

The crystal converted titanylphthalocyanine crystals just beforefiltration in Examples 1 to 3 and Comparative Examples 1 to 3 wereobserved by a TEM in the same method of the water paste after dilutedwith the respective crystal conversion solvents so as to have 1% byweight. The average particle sizes are shown in Table 1. Different fromthe water pastes, the titanylphthalocyanine crystals prepared in

Examples 1 to 3 and Comparative Examples 1 to 3 had different forms suchas forms close to a triangle and forms close to a quadrangle. Therefore,the longest diagonal of the crystal was determined as the major axis.

TABLE 1 Average Particle Size (μm) Remarks Example 1 0.14 The particlesizes were almost uniform. Example 2 0.12 The particle sizes were almostuniform. Example 3 0.15 The particle sizes were almost uniform.Comparative Example 1 0.16 The particle sizes were almost uniform.Comparative Example 2 0.25 The particle sizes included large sizes Offrom about 0.3 to 0.4 μm. Comparative Example 3 0.38 The particle sizesincluded huge sizes not less than 0.5 μm.

A part of the water paste prepared in Example 1 was dried at 80° C.under a reduced pressure (5 mm Hg) for 2 days to prepare atitanylphthalocyanine powder having a low crystallinity.

X-ray diffraction spectra of the dried powder and thetitanylphthalocyanine crystals prepared in Examples 1 to 3 andComparative Examples 1 to 3 were measured by the following conditions.

X-ray tube: Cu

Voltage: 40 kV

Current: 20 mA

Scanning speed: 1°/min

Scanning range: 3 to 40°

Time constant: 2 sec

The X-ray diffraction spectrum of the dried powder of the water paste isshown in FIG. 8.

Because the titanylphthalocyanine crystals prepared in Examples 1 to 3and Comparative Examples 2 and 3 had the same X-ray diffraction spectra,the X-ray diffraction spectrum of the titanylphthalocyanine crystalprepared in Example 1 is shown in FIG. 9 as a representative example.

The titanylphthalocyanine crystal prepared in Comparative Example 1 hada different X-ray diffraction spectrum from those of the Examples 1 to 3and Comparative Examples 2 and 3, i.e., had a minimum angle at 7.5°.This is shown in FIG. 10.

Comparative Example 4

A pigment was prepared in accordance with a method disclosed in Japaneselaid-Open Patent Publication No. 1-299874. Namely, the wet cake (waterpaste) prepared in Example 1 was dried and 1 g of the dried material wasincluded in 50 g of polyethylene glycol. The mixture was dispersed by asand mill for 1 hr with 100 g of glass beads. After the crystalconversion, the dispersed material was washed with a diluted sulfuricacid and a aqueous solution of ammonium hydroxide in this order anddried to prepare a pigment. This is a Pigment 7.

Comparative Example 5

A pigment was prepared in accordance with a method disclosed in Japaneselaid-Open Patent Publication No. 3-269064. Namely, the wet cake preparedin Example 1 was dried, and after 1 g of the dried material was stirredin a mixed solvent of 10 g of ion exchange water and 1 g ofmonochlorobenzene for 1 hr at 50° C., the mixture was washed withmethanol and ion exchange water and dried to prepare a pigment. This isa Pigment 8.

Comparative Example 6

A pigment was prepared in accordance with a method disclosed in Japaneselaid-Open Patent Publication No. 2-8256. Namely, 9.8 g ofphthalodinitrile and 75 ml of 1-chloronaphthalene were mixed andstirred, and a 2.2 ml of titanium tetrachloride was dropped in themixture under a nitrogen gas stream. The mixture was gradually heated tohave a temperature of 200° C. and stirred for 3 hrs while the reactiontemperature was maintained at 200 to 220° C. Then, the mixture wascooled to have a temperature of 130° C. and filtered to prepare apowder. After the powder was washed to have a blue color with1-chloronaphthalene, methanol for several times and hot water having atemperature of 80° C. for several times, the powder was dried to preparea pigment. This is a Pigment 9.

Comparative Example 7

A pigment was prepared in accordance with a method disclosed in Japaneselaid-Open Patent Publication No. 64-17066. Namely, 5 parts of α-typeTiOPc was subjected to a crystal conversion treatment by a sand grinderwith 10 g of salt and 5 g of acetophenone at 100° C. for 10 hrs. Themixture was washed with ion exchange water and methanol and refined withan aqueous solution of a diluted sulfuric acid. Then, the mixture waswashed with ion exchange water again not to have a acid content, anddried to prepare a pigment. This is a Pigment 10.

Comparative Example 8

A pigment was prepared in accordance with a method disclosed in Japaneselaid-Open Patent Publication No. 11-5919. Namely, after 20.4 parts ofo-phthalodinitrile and 7.6 parts of titanium tetrachloride were heatedin 50 parts of quinoline at 200° C. for 2 hrs, the solvent was removedfrom the mixture by a steam distillation. The mixture was refined with achloride aqueous solution having a concentration of 2% and a sodiumhydroxide aqueous solution having a concentration of 2%. Then, themixture was washed with methanol and N,N-dimethylformamide, and dried toprepare 21.3 parts of titanylphthalocyanine. 2 parts of thetitanylphthalocyanine was gradually dissolved in 40 parts of sulfuricacid having a concentration of 98% and a temperature of 5° C., and themixture was stirred for about 1 hr while the temperature of 5° C. wasmaintained. Then, the mixture was slowly included in 400 parts of icedwater in which a sulfuric acid was mixed and stirred at a high speed,and a precipitated crystal was filtered. The crystal was washed withdistilled water not to have an acid content to prepare a wet cake. Thewet cake including a supposed content of 2 parts of phthalocyanine wasstirred in 100 parts of tetra hydrofuran for about 5 hrs. The mixturewas filtered, washed and dried to prepare a pigment. This is a Pigment11.

X-ray diffraction spectra of the pigments prepared in ComparativeExamples 4 to 8 were measured by the same method used for the pigmentsprepared in Examples 1 to 3 and Comparative Examples 1 to 3 to find thatthe spectra were the same spectra disclose in respective Publications.Table 2 which is similar to Table 1 shows evaluation results of thepigments prepared in Comparative Examples 4 to 8.

TABLE 2 Average Particle Size (μm) Remarks Crystal Form Comparative 0.18The particle sizes The crystal form Example 4 were almost was differentfrom uniform. that of Example 1, not having a peak at 9.4° and 9.6°.Comparative 0.23 The particle sizes The crystal form Example 5 includedlarge was different from sizes of from that of Example 1, about 0.3 to0.4 not having a peak at μm. 7.3°. Comparative 0.36 The particle sizesThe crystal form Example 6 included huge was different from sizes notless that of Example 1, than 0.5 μm. not having an apparent peak at 9.4°and 9.6°. Comparative 0.20 The particle sizes The crystal form Example 7were almost was different from uniform. that of Example 1, having a peakat 7.5°. Comparative 0.56 The particle sizes The crystal form Example 8included huge was different from sizes not less that of Example 1, than0.5 μm. having a peak at 7.5° and an overlapped peak at 9.4° and 9.6°.

Example 4

The following components were dispersed with a commercial beads milldisperser using a PSZ ball having a diameter of 0.5 mm at a rotorrevolution speed at 1,500 rpm and the dispersion was stopped when thevolume-average particle diameter was less than 0.2 μm to prepare adispersion liquid. This is a Dispersion Liquid 1.

Titanylphthalocyanine crystal 15 prepared in Example 1 (Pigment 1)Polyvinylbutyral 10 (BX-1 from Sekisui Chemical Co., Ltd.) 2-butanone280

Example 5

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 2 to prepare a dispersion liquid. This is a Dispersion Liquid 2.

Example 6

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 3 to prepare a dispersion liquid. This is a Dispersion Liquid 3.

Example 7

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 4 to prepare a dispersion liquid. This is a Dispersion Liquid 4.

Comparative Example 9

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 5 to prepare a dispersion liquid. This is a Dispersion Liquid 5.

Comparative Example 10

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 6 to prepare a dispersion liquid. This is a Dispersion Liquid 6.

Comparative Example 11

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 7 to prepare a dispersion liquid. This is a Dispersion Liquid 7.

Comparative Example 12

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 8 to prepare a dispersion liquid. This is a Dispersion Liquid 8.

Comparative Example 13

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 9 to prepare a dispersion liquid. This is a Dispersion Liquid 9.

Comparative Example 14

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 10 to prepare a dispersion liquid. This is a Dispersion Liquid10.

Comparative Example 15

The procedures of preparation for the dispersion liquid in Example 4were repeated except for changing the titanylphthalocyanine crystal toPigment 11 to prepare a dispersion liquid. This is a Dispersion Liquid11.

Comparative Example 16

The procedures of preparation for the dispersion liquid in ComparativeExample 10 were repeated except for stopping the dispersion before thecrystal form changes. This is a Dispersion Liquid 12.

Particle sizes (volume-average particle diameter) of the pigments in thedispersion liquids prepared in Examples 4 to 7 and Comparative Examples9 to 16 were measured by CAPA700 from Horiba, Ltd. In addition, X-raydiffraction spectra of powders prepared by drying and hardening thedispersion liquids were measured. The results are shown in Table 3.

TABLE 3 Volume-Average Particle Diameter (μm) XD Diffraction SpectrumExample 4 0.18 Same before dispersion. (Dispersion Liquid 1) Example 50.19 Same before dispersion. (Dispersion Liquid 2) Example 6 0.18 Samebefore dispersion. (Dispersion Liquid 3) Example 7 0.18 Same beforedispersion. (Dispersion Liquid 4) Comparative 0.19 Changed to a spectrumshown in FIG. Example 9 11 (Dispersion Liquid 5) Comparative 0.20Changed to a spectrum shown in FIG. Example 10 11 (Dispersion Liquid 6)Comparative 0.19 Same before dispersion. Example 11 (Dispersion Liquid7) Comparative 0.18 Changed to a spectrum shown in FIG. Example 12 11(Dispersion Liquid 8) Comparative 0.20 Changed to a spectrum shown inFIG. Example 13 11 (Dispersion Liquid 9) Comparative 0.19 Same beforedispersion. Example 14 (Dispersion Liquid 10) Comparative 0.20 Changedto a spectrum shown in FIG. Example 15 11 (Dispersion Liquid 11)Comparative 0.40 Same before dispersion. Example 16 (Dispersion Liquid12)

A new peak indicated by an arrow in FIG. 11 appeared. A part of thecrystal form changed to another crystal form.

Example 8

An undercoat layer coating liquid, a CGL coating liquid and CTL coatingliquid having the following components were coated and dried in thisorder on an aluminium cylinder having a diameter of 60 mm (JIS1050) as asubstrate to prepare a multilayer photoreceptor having an undercoatlayer 3.5 μm thick, a CGL 0.2 μm thick and a CTL 25 μm thick.

Undercoat layer coating liquid Titanium oxide 70 (CR-EL from IshiharaSangyo Kaisha, ltd.) Alkyd resin 15 (Bekkolite M6401-50-S (solid content50%) from Dainippon Ink And Chemicals, inc.) Melamine resin 10 (SuperBekkamin L-121-60 (solid content 60%) from Dainippon Ink And Chemicals,inc.) 2-butanone 100

CGL Coating Liquid

The Dispersion Liquid 1 was used.

CTL coating liquid Polycarbonate 10 (Iupilon Z300 from Mitsubishi GasChemical Co., Inc.) CTM having the following formula  7

Methylene chloride 80

Example 9

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 2 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Example 10

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 3 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Example 11

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 4 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Comparative Example 17

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 5 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Comparative Example 18

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 6 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Comparative Example 19

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 7 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Comparative Example 20

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 8 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Comparative Example 21

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 9 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Comparative Example 22

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 10 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Comparative Example 23

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 11 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

Comparative Example 24

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for using the Dispersion Liquid 12 as a CGL coatingliquid instead of the Dispersion Liquid 1 to prepare a photoreceptor.

The thus prepared electrophotographic photoreceptors in Examples 8 to 11and comparative Examples 17 to 24 were installed in theelectrophotographic apparatus in FIG. 3, which uses a LD having awavelength of 780 nm as an imagewise light irradiator (with a polygonmirror) and a contact charging roller as a charger, and images wereproduced in the following charging conditions:

DC bias: approximately −1,600 V (an unexposed part potential of thephotoreceptors was −900 V)

20,000 images of a chart having a written part of 6% were continuouslyproduced, and an initial image and an image after production of 20,000images were evaluated. Specifically, a white mat image was produced inthe initial stage and after 20,000 images were produced to evaluatebackground fouling thereof as shown in Table 4.

In addition, at the same time, a jig was used such that an electrometerwas set at a position where the image developer was installed so as tomeasure surface potential of the photoreceptor (a solid image developedportion thereof). The results of the surface potential of thephotoreceptor in the initial stage and after 20,000 images were producedare shown in Table 4.

TABLE 4 Surface Potential Images (−V) After After Dispersion 20,00020,000 Liquid Initial images Initial images Ex. 8 1 5 4 120 135 Ex. 9 25 4 120 135 Ex. 10 3 5 4 120 135 Ex. 11 4 4 3 130 145 Com. Ex. 17 5 4 3140 180 Com. Ex. 18 6 4 3 150 200 Com. Ex. 19 7 4 2 130 160 Com. Ex. 208 4 3 140 185 Com. Ex. 21 9 4 2 150 195 Com. Ex. 22 10 4 2 125 155 Com.Ex. 23 11 4 2 135 170 Com. Ex. 24 12 3 2 130 140 Background foulinglevel: 5: Almost no background fouling 4: Slight background fouling 3:Limit level for practical use 2 or less: Impossible level for practicaluse

Example 12

The procedures of preparation for the photoreceptor in Example 8 wererepeated except for changing the CTL coating liquid to a CTL coatingliquid having the following components to prepare a photoreceptor.

CTL coating liquid Polymer CTM having the following formula andapproximate weight-average molecular weight of 140,000 10

Additive having the following formula 0.5

Methylene chloride 100

Example 13

The procedures of preparation for the photoreceptor in Example 8 wererepeated except that the thickness of the CTL was changed to 22 μm and aprotection layer coating liquid having the following components wascoated and dried on the CTL to form a protection layer having athickness of 3 μm thereon.

Protection layer coating liquid Polycarbonate  10 (Iupilon Z300 fromMitsubishi Gas Chemical Co., Inc.) CTM having the following formula  7

α-Alumina fine particles having a resistivity of  4 2.5 × 10¹² Ω · cmand an average primary particle diameter of 0.4 μm Cyclohexanone 500Tetrahydrofuran 150

Example 14

The procedures of preparation for the photoreceptor in Example 8 wererepeated except that the thickness of the CTL was changed to 22 μm and aprotection layer coating liquid having the following components wascoated and dried on the CTL to form a protection layer having athickness of 3 μm thereon.

Protection layer coating liquid Polycarbonate  10 (Iupilon Z300 fromMitsubishi Gas Chemical Co., Inc.) CTM having the following formula  7

Titanium oxide fine particles having a resistivity of  4 1.5 × 10¹⁰ Ω ·cm and an average primary particle diameter of 0.5 μm Cyclohexanone 500Tetrahydrofuran 150

Example 15

The procedures of preparation for the photoreceptor in Example 8 wererepeated except that the thickness of the CTL was changed to 22 μm and aprotection layer coating liquid having the following components wascoated and dried on the CTL to form a protection layer having athickness of 3 μm thereon.

Protection layer coating liquid Polycarbonate  10 (Iupilon Z300 fromMitsubishi Gas Chemical Co., Inc.) CTM having the following formula  7

Tin oxide-antimony oxide powder having a resistivity of  4 10⁶ Ω · cmand an average primary particle diameter of 0.4 μm Cyclohexanone 500Tetrahydrofuran 150

Example 16

The procedures of preparation for the photoreceptor in Example 8 wererepeated except that the thickness of the CTL was changed to 22 μm and aprotection layer coating liquid having the following components wascoated and dried on the CTL to form a protection layer having athickness of 3 μm thereon.

Protection layer coating liquid Polymer CTM having the following formulaand approximate weight-average molecular weight of 140,000 17

Alumina fine particles having a resistivity of 2.5 × 10¹² Ω · cm and anaverage primary particle diameter of 0.4 μm  4 Cyclohexanone 500Tetrahydrofuran 150

The thus prepared electrophotographic photoreceptors in Examples 8 and12 to 16 were installed in the electrophotographic apparatus in FIG. 3,which uses a LD having a wavelength of 780 nm as an imagewise lightirradiator (with

a polygon mirror) and a contact charging roller as a charger, and imageswere produced in the following charging conditions:

DC bias: approximately −1,600 V (an unexposed part potential of thephotoreceptors was −900 V)

50,000 images of a chart having a written part of 6% were continuouslyproduced, and an initial image and an image after production of 50,000images were evaluated. Specifically, a white mat image was produced inthe initial stage and after 20,000 images were produced to evaluatebackground fouling thereof as shown in Table 5.

In addition, after 50,000 images were produced, 50 images were producedin an environment of a temperature at 30° C. and a humidity at 90% RH.

Further, surface abrasion amounts of the photoreceptors were measuredafter 50,000 images were produced.

The results are shown in Table 5.

TABLE 5 Background Fouling Image Abrasion After After 30° C./90% AmountInitial 50,000 50,000 RH (μm) Ex. 8 5 3 Image Image 3.1 density densityslightly slightly lowered lowered Ex. 12 5 3 to 4 Good Good 1.5 Ex. 13 54 to 5 Good Good 0.6 Ex. 14 5 4 to 5 Good Good 0.6 Ex. 15 5 4 SlightlyBlurred 0.7 blurred Ex. 16 5 5 Good Good 0.4 Background fouling level:5: Almost no background fouling 4: Slight background fouling 3: Limitlevel for practical use 2 or less: Impossible level for practical use

Example 17

The photoreceptor prepared in Example 8 was installed in theelectrophotographic apparatus in FIG. 3, which uses a LD having awavelength of 780 nm as an imagewise light irradiator (with a polygonmirror) and a charger located closely to the photoreceptor in FIG. 4 (agap there between was 50 μm), which was a charging roller having a woundinsulative tape 50 μm thick at both ends thereof. Images were producedin the following charging conditions:

DC bias: approximately −1,650 V (an unexposed part potential of thephotoreceptors was −900 V)

20,000 images of a chart having a written part of 6% were continuouslyproduced, and an initial image and an image after production of 20,000images were evaluated. After 20,000 images were produced, a halftoneimage was produced to evaluate.

Example 18

The procedures of evaluation for the photoreceptor in Example 17 wererepeated except for changing the charging conditions as follows:

DC bias: −900 V

AC bias: 2.0 kV (peak to peak)

Frequency: 1.5 kHz

Example 19

The procedures of evaluation for the photoreceptor in Example 18 wererepeated except for changing the thickness of the insulative tape andthe gap from 50 to 150 μm.

Example 20

The procedures of evaluation for the photoreceptor in Example 18 wererepeated except for changing the thickness of the insulative tape andthe gap from 50 to 250 μm.

The results are shown in Table 6 including those of Example 8.

TABLE 6 Halftone Image Remarks Example 8 Slightly nonuniform Chargingroller is observably contaminated Example 17 Slightly nonuniform Nocharging roller contamination Example 18 No nonuniform No chargingroller contamination Example 19 No nonuniform No charging rollercontamination Example 20 Slightly nonuniform No charging rollercontamination

Example 21

The procedures of preparation for the photoreceptor in Example 8 wererepeated to prepare a photoreceptor except for changing the substrate toan aluminium cylinder having a diameter of 30 mm (JIS1050).

Example 22

The procedures of preparation for the photoreceptor in Example 21 wererepeated to prepare a photoreceptor except that the aluminium cylinderwas subjected to the following anodic oxide coating without forming theundercoat layer.

Anodic Oxide Coating

A surface of the cylinder was abraded to have a mirror finished surface,and degreasing cleaning and water washing were performed on thecylinder. Then, the cylinder was dipped in an electrolyte including asulfuric acid of 15% by volume and having a temperature of 20° C. toperform an anodic oxide coating at a bath voltage of 15 V for 30 min.Further, the cylinder was washed with water and sealed with an aqueoussolution of nickel acetate (50° C.) having a concentration of 7%. Then,the cylinder was washed with purified water to prepare a substratehaving an anodic oxide coated layer having a thickness of 6 μm.

Comparative Example 25

The procedures of preparation for the photoreceptor in ComparativeExample 17 were repeated to prepare a photoreceptor except for changingthe substrate to an aluminium cylinder having a diameter of 30 mm(JIS1050).

Comparative Example 26

The procedures of preparation for the photoreceptor in ComparativeExample 24 were repeated to prepare a photoreceptor except for changingthe substrate to an aluminium cylinder having a diameter of 30 mm(JIS1050).

The thus prepared photoreceptors in Examples 21 and 22 and ComparativeExamples 25 and 26 were installed in the cartridge for anelectrophotographic apparatus in FIG. 6, and the cartridge was installedin the electrophotographic

apparatus in FIG. 7, which uses a LD having a wavelength of 780 nm as animagewise light irradiator (with a polygon mirror) and a charger locatedclosely to the photoreceptor in FIG. 4 (a gap there between was 50 μm),which was a charging roller having a wound insulative tape 50 μm thickat both ends thereof. Images were produced in the following chargingconditions:

DC bias: approximately −800 V

AC bias: 1.8 kV (peak to peak)

Frequency: 1.5 kHz

20,000 images of a full-color chart having a written part of 6% werecontinuously produced, and an initial image and an image afterproduction of 20,000 images were evaluated. Specifically, a white matimage was produced in the initial stage and after 20,000 images wereproduced to evaluate background fouling thereof. In addition, a chartfor color reproducibility evaluation was used to evaluate colorreproducibility of an image after 20,000 images were produced. Theresults are shown in Table 7.

TABLE 7 Background Fouling Color Initial After 20,000 ReproducibilityEx. 21 5 3 to 4 Good Ex. 22 5 4 to 5 Good Com. Ex. 5 3 Color balance was23 lost Com. Ex. 4 2 Good 24 Background fouling level: 5: Almost nobackground fouling 4: Slight background fouling 3: Limit level forpractical use 2 or less: Impossible level for practical use

Finally, whether the minimum diffraction peak at a lowest Bragg (2 θ)angle of 7.3° of the titanylphthalocyanine crystal of the presentinvention is different from peaks at 7.5° of known materials will beverified.

Measurement Example 1

Three % by weight of a pigment prepared by a method disclosed inJapanese Laid-Open Patent Publication No. 61-239248 (having a maximumdiffraction peak at 7.5°) was included in the pigment prepared inExample 1 (having a minimum

diffraction peak at 7.3°). The mixture was mixed in a mortar and anX-ray spectrum thereof was measured. The results are shown in FIG. 12.

Measurement Example 2

Three % by weight of a pigment prepared by a method disclosed inJapanese Laid-Open Patent Publication No. 61-239248 (having a maximumdiffraction peak at 7.5°) was included in the pigment prepared inComparative Example 1 (having a minimum diffraction peak at 7.5°). Themixture was mixed in a mortar and an X-ray spectrum thereof wasmeasured. The results are shown in FIG. 13.

The spectrum in FIG. 12 has two independent peaks at low angles of 7.3and 7.5°, and they are different from each other. The spectrum in FIG.13 has only one peak at a low angle of 7.5°, and is apparently differentfrom the spectrum in FIG. 12.

Consequently, the minimum diffraction peak at a lowest Bragg (2 θ) angleof 7.3° of the titanylphthalocyanine crystal of the present invention isdifferent from peaks at 7.5° of known titanylphthalocyanine crystals.

In this application several X-ray features of preferred materials aredescribed. For example, the phrase “preferably no diffraction peak isobserved at an angle greater than 7.3° and less than 9.4°” is usedthroughout to describe preferred spectrum characteristics. It should benoted, however, that all spectrum peaks have a certain variation in peakassignment that typically depends upon the accuracy and repeatability ofthe instrument. In many cases, variation is as little as 0.02 degrees,or less. Thus, where peaks positions are specified herein they may havea position variation of plus or minus 0.2 degrees, more preferably plusor minus 0.1 degrees, including all of 0.05, 0.02, etc. degrees. Thus,in practicality the phrase “no diffraction peak is observed at an anglegreater than 7.3° and less than 9.4°” is meant to set a minimum intervalbetween the required peaks at 7.3 and 9.4 of 2.0 degrees absolute ormore where no peak is present.

This document claims priority and contains subject matter related toJapanese Patent Application No. 2002-172496 filed on Jun. 13, 2002,incorporated herein by reference.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit and scope of theinvention as set forth therein.

1-19. (canceled) 20: A crystalline pigment comprisingtitanylphthalocyanine and tetra hydrofuran or toluene; wherein saidcrystalline pigment has a CuKα 1.542 Å X-ray diffraction spectrumcomprising plural diffraction peaks and a primary particle diameter notgreater than 0.2 μm, wherein a maximum diffraction peak is observed at aBragg (2θ) angle of 27.2°; main peaks are observed at 9.4°, 9.6° and24.0°; and a minimum diffraction peak is observed at 7.3°; and nodiffraction peak is observed at an angle greater than 7.3° and less than9.4°, wherein said angles may vary by ±0.2° and the minimum intervalwhere no peak is observed between required peaks at 7.3 and 9.4 is 2.0degrees absolute or more, and wherein no diffraction peak is observed at26.3°. 21: An electrophotographic photoreceptor comprising: anelectroconductive substrate; a charge generation layer located overlyingthe electroconductive substrate and comprising the crystalline pigmentaccording to claim 20; and a charge transport layer located overlyingthe charge generation layer. 22: The electrophotographic photoreceptorof claim 21, wherein the charge transport layer comprises a chargetransport polymer material. 23: The electrophotographic photoreceptor ofclaim 21, further comprising a protection layer located overlying thecharge transport layer. 24: The electrophotographic photoreceptor ofclaim 22, wherein the protection layer comprises at least one of aninorganic pigment and a metal oxide, which have a resistivity not lessthan 10¹⁰ Ω·cm. 25: The electrophotographic photoreceptor of claim 24,comprising a metal oxide selected from the group consisting of alumina,titanium oxide and silica. 26: The electrophotographic photoreceptor ofclaim 23, wherein the protection layer comprises a charge transportpolymer material. 27: The electrophotographic photoreceptor of claim 21,wherein an oxide film is formed on the substrate by anodizing. 28: Animage forming method comprising; charging the electrophotographicphotoreceptor according to claim 21; irradiating the electrophotographicphotoreceptor with imagewise light to form an electrostatic latent imagethereon; developing the electrostatic latent image with a developercomprising a toner to form a toner image thereon; and transferring thetoner image onto a transfer sheet. 29: An image forming apparatuscomprising; at least one image forming unit comprising; theelectrophotographic photoreceptor according to claim 21; a chargerconfigured to charge the electrophotographic photoreceptor; anirradiator configured to irradiate the electrophotographic photoreceptorwith imagewise light to form an electrostatic latent image thereon; animage developer configured to develop the electrostatic latent imagewith a developer comprising a toner to form a toner image thereon; and atransferer configured to transfer the toner image onto a transfer sheet.30: The image forming apparatus of claim 29, comprising plural imageforming units. 31: The image forming apparatus of claim 29, wherein thecharger is contacted or located close to the electrophotographicphotoreceptor. 32: The image forming apparatus of claim 31, wherein thecharger is located close to the electrophotographic photoreceptor and agap between the charger and the electrophotographic photoreceptor is notgreater than 200 μm. 33: The image forming apparatus of claim 29,wherein the charger applies a DC voltage overlapped with an AC voltageto the electrophotographic photoreceptor. 34: A process cartridge for animage forming apparatus, comprising; the electrophotographicphotoreceptor according to claim 21; and at least one of: a chargerconfigured to charge the electrophotographic photoreceptor; anirradiator configured to irradiate the electrophotographic photoreceptorwith imagewise light to form an electrostatic latent image thereon; animage developer configured to develop the electrostatic latent imagewith a developer comprising a toner to form a toner image thereon; atransferer configured to transfer the toner image onto a transfer sheet;a cleaner configured to clean the photoreceptor after the toner image istransferred into the transfer sheet; and a discharger configured todischarge charges remaining on the photoreceptor after the toner imageis transferred into the transfer sheet. 35: A method of producing thecrystalline pigment of claim 20 comprising: subjecting atitanylphthalocyanine, which is either amorphous or low-crystalline, andwhich has a maximum CuKα 1.542 Å diffraction peak having a half widthnot less than 1° at a Bragg (2 θ) angle of from 7.0 to 7.5°±0.2° and anaverage primary particle diameter not greater than 0.1 μm, to crystalconversion with an organic solvent in the present of water; andseparating the titanylphthalocyanine from the organic solvent before thetitanylphthalocyanine crystal grows to a size where the average primaryparticle diameter is greater than 0.2 μm; wherein the organic solvent isselected from the group consisting of tetra hydrofuran, toluene, anddichloromethane. 36: The crystalline pigment of claim 20, wherein thepigment comprises tetra hydrofuran. 37: The crystalline pigment of claim20, wherein the pigment comprises toluene.